This is part 1 of a 2 part image/story.
Link for part 2:
https://www.furaffinity.net/view/39078666/

— Do I really have to put this collar? — Cassie frowned at the silly trinket — Can’t you just do your hypnosis stuff without it?
— I wish I could — Tyler gave her an embarrassed smile — But you have too much of a dominant personality for me to tame. The collar will tone that down a little.
— This is a pet’s collar…
— Exactly — he rubbed his hands — That’s the point.
— Listen, Tyler — she sighed — I know I can be a little bossy sometimes… And a little pushy… And a bit aggressive… And…
— Cassie… please…
— If you don’t like me the way I am…
— Cassie! — he spoke a bit louder — I love you! But some days you are a little too harsh on me. Sometimes you don’t know when to stop before I’m actually hurt. I know you are strong and assertive, and I love those qualities about you, but…
— But sometimes you want to sit on the throne for a bit — she rolled her eyes — I mean… I can cut you some slack if you want to.
— We tried… It didn’t work.
— Really?
— Do you remember Tyler’s day? The day of the week you’ve agreed to tone down your assertiveness so I could relax?
— Was it… sunday? monday?
— It was tuesdays. Today — he sighed — You didn’t follow it for a single month...
— Oh… sorry — she showed her tongue, playfully.
— I really like strong women who are in charge of stuff. However, there are times when I’m frustrated and feeling helpless. Some days I want to reverse the roles and feel a bit of a morale boost, you know?
— We can always roleplay, if you want to — she winked.
— We’ve tried it…
— Really?
— Remember when we roleplayed a kidnapping?
— Oh! — she laughed — Yeah.
— You tied me up!
— Exactly… It was a kidnapping.
— I was the kidnapper!
— Sorry — she gave a “not sorry” smirk.
— Remember when we roleplayed big bad wolf and scout girl?
— Well… Was it that time when I made you fetch a stick for me?
— Somehow… yes — he blushed — Remember the captive princess and dark knight roleplay? The teacher and the student who needed to pass? The innocent native and the pirate captain? The inquisitor and the witch? The…
— Okay… okay… I’m sorry — she raised both hands — I guess it’s just in my nature. Whenever you lower your guard, I just happen to reverse the roles.
— You purposely lower my guard.
— It’s my thing…
— That’s why I’m trying hypnosis today.
— Aren’t you scared that maybe you might get hypnotised instead?
— That’s why I brought this collar.
— How about you put this collar on yourself and become my little puppy for the day? — she gently bit his lips while slowly taking the collar from his hands — I’ll take good care of you.
— Stop tempting me… please — he gulped and snatched the collar back — That’s exactly what I was talking about ten seconds ago. Can you try to cooperate today? It’s Tyler’s day!
— Alright, alright — she stepped back — I’ll cooperate… woofy woofy…
— Okay — Tyler took a deep breath — For this to work, you must put up a bit of effort. Do as I say and don’t try anything funny, alright?
— I’ll try.
— Do as I say, no questions asked. Okay?
— Hmmm… Fine?
— Now relax and let me put this collar on you.
Tyler approached her, holding the collar with both hands. Suddenly Cassie bit his arm.
— H-hey!
— I couldn’t resist — she laughed, holding her belly — Your face was priceless.
— What did I just say about cooperation?
— Sorry… Sorry — she put her hands behind her back — I’ll behave.
Tyler sighed, then tried again. He passed the collar around Cassie’s neck, then closed it.
— Too tight?
— No — she said.
— What about now? — He tightened the collar a bit more.
— Yeah… now I can feel it — she scratched the collar with a finger.
— Okay. A bit more then — he tightened it a bit more.
— H-hey! I said it was alright! — Cassie held his hands.
— I know — he smiled — But does it hurt?
— N-no… not really… but it’s kinda tight… It’s uncomfortable.
— You are supposed to feel it.
— It feels strange when I gulp.
— Then it’s perfect — he smiled — You look cute with it.
— Shut up…
— Now, close your eyes.
Cassie obeyed.
— From this point on, don’t talk unless I ask you to. Understood?
She nodded.
— Good girl — Tyler gave her a pet on the head.
Cassie smiled.
— I want you to concentrate on this pressure around your neck. This pressure is there to remember you of the collar. This pressure is there because you belong to someone.
Cassie thought of how much she disliked that collar. How much she wanted to just jump on Tyler and pin him against the floor. How much she wanted to force that collar on her boyfriend and tell him to bark for her. Yet she didn’t move.
— As long as you are wearing this collar, you belong to me. This constant pressure is a reminder of that. A pressure that you will learn to like… Even love it. This collar makes you want to behave. This collar makes you want to be obedient. This collar that presses against your neck makes you feel good. It makes you feel loved. You love belonging to me. You love having an owner that takes good care of you. You love being called a good girl.
Cassie closed her fists and bit her lips. Those were all things she wanted to tell Tyler, not the other way around. He was her pet. She was her owner. She wanted not only to put that damn collar on him, but also to tie it to a leash and force him to walk on his fours. Yet she didn’t move. Yet she remained silent.
— It feels good to belong to me. It takes the weight off your shoulders. You don’t have to worry about anything, because I’ll worry instead. You don’t have to decide anything, because I’ll decide it instead. You don’t have to question anything, because obeying is easier. You don’t have to resist, because giving up is relaxing. Thinking is too much work… You are too tired to think. This pressure in your neck tells you not to worry. This pressure in your neck tells you not to question. This pressure in your neck tells you to obey. It’s easy. It’s relaxing. It’s refreshing. It’s liberating. You feel much lighter when you just let go. You love being called a good girl.
Cassie was trying to relax, but that thing in her neck was extremely bothersome. She wanted to take it out. It was dumb. She felt ridiculous wearing that crap. Yet she didn’t move.
— Bark for me.
— Woof!
Cassie opened her eyes, surprised.
— Good girl — Tyler said. Then scratched her behind the ear.
— This is embarrassing — she blushed.
— That’s the point — he gave her a friendly smile — I’m taking away your assertiveness, little by little. The whole process will make you very embarrassed… Humiliated… Ashamed. You'll like it.
— I’m not sure it’s gonna work.
— It is already working — he chuckled — If it wasn't, you would’ve taken this collar out and forced it into me by now.
— Can't argue with that…
— Now close your eyes again.
She obeyed.
— Good girl.
Cassie smiled.
— I can't force you to do anything you don’t want to, Cassie. Instead I'll just make you realize how much you like it. How good it feels to be overpowered by someone else. How good it feels to give up without resisting. How good it feels to be on the other side. How good it feels when your owner calls you a good girl.
She was indeed curious about how Tyler felt. She always pushed and playfully bullied her boyfriend, yet he seemed to enjoy it. Maybe there was something good about being submissive. She always wondered what it would feel like. She remembered Tyler’s happy face whenever she overwhelmed him. What did he feel during those times? How could he find so much joy in being played by her?
— Bark for me.
— Woof!
— Good girl — he petted her head.
Cassie’s heart melted a bit.
“What the hell am I doing?”
— You are probably thinking what the hell you are doing right now. But don’t worry. That’s just your dominant self trying to speak. You don’t want her right now. She’s going to take away your fun. She's going to take control of you! But you don’t want to be under her control. You are a strong and independent girl who can’t be controlled by her. She’s going to take away this smile from your face. You don’t want that, right? You are a good girl! Bark for me.
— Woof!
— Good girl — he caressed her neck.
“I can’t be controlled!”
— She can’t control you right now. You won’t let her do that. Because you have an owner now and nobody besides him has any say on what you can and can’t do. You are already feeling a lot better without her. You are free. You feel light and relaxed. It’s so good to be free... Sit!
Cassie sat on her butt immediately.
— Good girl — Tyler poked her nose.
She blushed and smiled.
— Concentrate on my voice. Concentrate on this pressure in your neck and how good it feels. Concentrate on this wonderful feeling of being owned and loved. Breathe in, slowly. Concentrate just in my voice. Breathe out, slowly. Don’t listen to these annoying thoughts in your head. Breath in. Right now you just want to relax more than anything. Breathe out. This is what you want and nobody can stop you from relaxing. Breathe out. Nobody can stop you from being someone’s pet. Breathe in. You want that. You’ll have that. Breathe out. That's how things always were for you. Bark for me!
— Woof!
— Good girl — he rubbed her back.
Cassie felt a bit silly. Yet she tried to ignore that. Wearing a collar… sitting on the floor… barking for her boyfriend… That’s what she wanted to do. She wanted to do those things because they felt good. It wasn’t because he was asking. It was because she wanted to.
— I’ll count to one hundred very slowly. You’ll breathe in at one number, then breathe out on the next number. One… Remember this pressure in your neck and how good it feels… two… Let this relaxing feeling take over you… three… Imagine your assertiveness going away with each breath out… four…
Tyler continued to count…
She continued to pay attention…
.
.
.
Twenty two…
Her inner thoughts faded away...
.
.
.
Fifty seven…
Tyler’s voice was the only thing that existed in the whole world...
.
.
.
Eighty nine...
Until her mind went blurry…

— Wake up now, Cassie — said Tyler — Slowly… No need to hurry.
She blinked a few times, waking up on the ground, legs bent against her chest and back against the wall. She had no idea how long she had been sleeping, but there was still daylight outside.
— I think I fell asleep — she said, slowly getting up and stretching out — Is it bad?
— Do you feel any different?
— Well — she raised an eyebrow — I feel rested.
— Anything else?
— I don’t think so — she shrugged — Maybe this thing doesn’t work against me.
— Wanna eat something? Are you hungry?
— A bit.
She started walking towards the kitchen. Tyler followed right behind her, both of them walking at the same painfully slow speed, yet she didn’t mind.
— What ya having, Cassie?
— Scrambled eggs with cheese, I guess.
— Can you make me some too?
— Alright.
Tyler stood right behind her all the time while she was walking around to get the ingredients and cook, following Cassie around with an unnervingly slow pace that somehow she tried her best to match.
After the meal was done, she sat on a chair and Tyler sat in front of her at the other end of the small table, then she finally noticed the thick string he was holding. That thing went from his hand all the way to her neck!
Cassie jumped from the chair and felt a gentle tug from the leash.
— What the hell, Tyler!? — she held the leash trying to figure out when he sneaked that thing onto her — How long have I been…
— Leashed? — he smiled — Since you were born. I just took hold of it today.
— Stop joking — she touched her neck and felt the tight collar still on it.
— Maybe you’ve got used to it — he chuckled.
— Okay… Stop it! — she got serious — I’m fine with the collar, but this leash is way too much! Take it out, now!
— I'm sorry — he looked down to his plate — But if I take it out, you'll just overpower me immediately... I don't really want that.
— What? — she gasped — You put this thing on me. You take them off.
— You want me to take it off? — he rested his cheeks on his palms — You look so cute demanding things.
— Take this thing off of me, Tyler! This is an order!
— Why don’t you take it out yourself?
— Fine! — she reached for her neck.
— But you’ll have troubles doing that with these clumsy paws.
Cassie ignored him and tried to remove the leash, yet she couldn’t untie it. She tried to remove the collar, but it seemed like the hardest dexterity puzzle of her life. The more she struggled to take it out, the more impossible it felt.
— Cassie. You need hands to take it out, not paws.
She then looked down at her “hands”.
Somehow those weren’t hands anymore. A thick layer of fur, the same color of her hair, had covered it entirely on the back side. Meanwhile, squishy and soft paw pads had appeared on her palms. Every finger was a lot shorter than usual and her thumb had retracted so much it was useless for any kind of manual task.
— Tyler! Stop it right now! This is an order!
— That’s not an order — he stood up — This is an order: Sit!
Cassie immediately sat on the floor, her butt pressing against the chilling marble.
— Good girl.
— Woof! — she put a hand against her mouth — What the hell?
— Obedient Cassie makes for a very good company. You are so docile now. I kind of like it when you are not threatening me.
— Take… this… collar… out… or… I’ll…
— Or you’ll what?
— I’ll lick your face until you take it out! — she growled, looking at him with angry eyes.
“I’m going to lick him so much. I’ll keep licking no matter how much he laughs or tells me to stop. I will show him!”
Cassie sprinted in his direction, half walking and half crawling. She jumped on Tyler and brought him down to the floor. Her poor boyfriend tried to defend himself, but was hopeless against her strength. She drenched his face with so much saliva Tyler looked as if he’d just got out of a shower. He couldn’t stop laughing.
“This is fun” She thought, while still licking his face “He’s got a nice sweet taste”
— I got you! — she laughed — You can’t escape me!
— You… ha... seem to… haha — Tyler was trying to speak while helplessly protecting his face — You seem to… haha… Be having a lot of f-hahahah… Fun… Look at your… ha ha… Look at your tail wagging!
— My what!? — she looked back. A long fluffy tail was peeking out of her skirt, wagging left and right like a happy puppy — The hell!?
She jumped back, her tail curling between her legs in fear as she grabbed it with both hands, examining that weird thing.
— This tail looks good on you — Tyler smiled — A good girl needs a good tail to show her master how happy she is.
— Shut up, Tyler! — she tried pulling it out, sure it was some kind of weird prop glued to her butt, yet it didn’t matter how hard she pulled, the thing wouldn’t come off. Worse than that, it began to hurt with all that effort — What did you do to me?
— I just made you more docile — he got up, cleaning his face with the sleeve — I had to make sure you would be more submissive than me... Maybe I went a little overboard, but you do look cute.
— Master, you are too mean! — she showed her sharp teeth.
— Nice teeth you have, Cassie. They look good with your puppy snout.
— My puppy snout? — she touched her muzzle and yelped. Her face was long and ended in a moist muzzle, much like a real dog — I’m gonna bite you, master! Stop making fun of me!
She got on her fours and appeared ready to jump on Tyler again.
— Sit!
Cassie obeyed.
— Woof!
— Good girl.
Her tail began wagging.
— Woof woof!
— You shouldn’t be this aggressive with your owner.
— Woof… sorry master! — she pressed her chin against the floor and covered her face with both hands — I’m not a good girl.
— Remember what I told you? — Tyler scratched her behind the ears — I told you to ignore this annoying voice in your head telling you to do bad things. Just focus on my voice and my commands. You’ll feel better this way. Understood?
— Woof! Yes!
— Lie down!
Cassie flopped on her back.
— Woof!
— Good girl!
Tyler started to tickle her unguarded belly. Cassie laughed with her tongue out and wagged her tail, moving her leg rapidly because of the tickling.
“He’s humiliating you! Make him pay for this!”
Cassie’s tail stopped and the girl looked confused.
“Bite his hand right now!”
Cassie showed her teeth again.
— Who’s a good girl?
— Woof! I am!
“No! No! You are not! You are not his pet!”
Tyler became more aggressive with his tickling, using both hands now, making Cassie laugh and wag her tail even more.
“I’m not a pet!”
— M-master! Stop! It's embarrassing!
“Wake up, girl! Bite him now!"
Cassie caught his wrist and pressed her teeth gently against it, biting it painlessly like a puppy trying to play.
— Wadda girl! You wanna play? — Tyler smiled and shook his arm — I guess you are really getting into the roleplay this time.
— P-play with me?
— Yeah! You want to play fetch?
"No! No! Heavens, No!"
— You want me to fetch something and bring it back to you? — she blushed.
— Precisely — he poked her muzzle — Like the good girl you are.
"I'm gonna kill you, Tyler!"
— I am a good girl?
— Yes you are! You are the best!
— Woof! — she gave Tyler a good lick on his cheek.
— Okay girl. Fetch! — he tossed a rubber ball across the living room and released her leash.
Cassie ran as fast as she could towards the ball, breathing through her mouth with her tongue out. She reached the ball and tried to grab it, but somehow she couldn't take it off the floor. Her paws were clumsy and not designed to hold stuff. She couldn't get the ball for her master.
— Master! I can't get it — she started sobbing.
— Use your mouth.
"Please wake up! Don't let him humiliate you like that!"
— M-master! That's humiliating. I'm not sure...
— Do it for me please? You are a good girl, aren't you?
— Woof! I am a good girl!
She caught the ball with her mouth and brought it back to Tyler, wagging her tail. At this point, Cassie was half walking and half crawling. He took the ball from her mouth and gave her a good belly rub.
— Good girl!
— Woof woof!
It felt so good to be called a good girl. That was such a strong validation for her. It signified her master's approval. If her master was happy, she was happy. No matter what he asked, she would do it, because his approval was the most important thing in her life. She wanted to be a proper dog for him. Master deserved a good dog!
— Master. I promise I'll be a good girl!
Cassie closed her eyes and focused on what she was lacking. Everything that she was missing to become a proper dog girl and make her master happy.
"Fur! I need more fur!"
She concentrated on that and a tickling sensation covered her skin, causing fur to grow all over her body, except for her belly and chest, which still had skin on it. She thought her master would find that attractive.
— Cassie! You don't have to go that far...
— Master deserves it!
She focused on her boring round ears, causing them to grow taller and pointier while also moving closer to the top of her head. That would allow her to better listen to her master’s commands.
— Cassie! Hey! What are you doing!?
— I want to become master's pet forever!
She stood on her fours while her whole body continued to reshape. Cassie still had a form that resembled a human, with round thighs, curvy waist, robust breasts and a semi-upright torso. However she had fur, paws instead of hands and feet, long ears, a snout, and a fluffy tail that never stopped wagging. She looked exactly like the kind of creature someone would conceive if asked to draw a cute human with dog features.
— Please, master! Make me your pet! I want to be your pet for the rest of my life — she grabbed him by his shoulders and began furiously licking his face — I want to play fetch, I want you to take me for a walk, I want belly rubs, I want to keep you company and learn funny tricks. I want to make you happy!
— C-Cassie! Please! — Tyler stepped back, yet she kept pressing against him, forcing him into the ground and licking him all over, spreading saliva everywhere. Somehow her assertiveness didn’t disappear, it had just transformed into something else. She was now overwhelming Tyler like she always did, but this time she was doing it to force him to humiliate and control her… She was a dominantly submissive?
— Give me an order, Master! Please! Any order! I exist to obey! — her body was shaking uncontrollably. Her pupils were huge and filled with passion — Do anything you want to me! Give me any order! Please master! Please!
— S-Sit! Sit!
Cassie jumped back and sat on the floor.
— Woof woof!
"He didn't say good girl! I did something wrong! What did I do wrong? I am not a good girl?"
— Master! I'm sorry!
— No No! Don't be sorry! You don't have to! You are a good girl!
— I'm a good girl! — she drooled. Somehow her body was euphoric and pulsating with pleasure. Those two simple words "good girl" were so powerful.
— Is this turning you on, Cassie? — Tyler blushed.
— Is it wrong?
— No... I guess it's working then... Better than it should.
— Of course it's working! Master is the best! He can do anything! That's why I love him! That's why I want to be his dog girlfriend forever!
— Okay okay. About that. You can't be like this forever. I'm sorry.
— Why not!? — she almost cried.
— Because I need old Cassie back. She's the girl I fell in love with.
— What about me!?
— I also love you. You are a good girl.
— Woof woof — she rolled on her back and put her tongue out, panting and drooling — But Cassie is mean to my master. He deserves better.
— I know… I know… But it’s time for you to go… I don’t want to risk messing up with her head too much.
— But I want to stay!
— Don't worry! I'll come back for you! I will never abandon you! Master loves you very much too. You are a good girl!
— Woof!
— You'll behave like a good girl and let Cassie come back, okay? But, whenever I say the words "good girl, come back" you will return to me immediately. Do you understand?
— Yes I do! I'll follow any order from master!
— Whenever I say "good girl, time to rest" you'll let Cassie take control and you will go back to the back of her mind until I call you again, alright?
— Yes!
— Good girl!
— Woof!
— When I say "good girl, come back" you will take over Cassie's mind and turn her body completely into the dog girl you are now. You'll think for her and she can't come back as long as you are happy! Okay?
— Yes!
— Good girl!
— Woof woof!
— But when I say "Good girl, time to rest" you'll immediately leave Cassie's mind. No matter what’s happening or how much you want to stay, you will let her come back. You'll also change her body back to human. Can you promise that?
— Yes! But I would rather be you dog girl forever!
— Do you promise that?
— Y-yes...
— Good girl.
— Woof!
Tyler petted her head and pressed his nose against her muzzle.
— I love you! — he smiled and snapped his finger — Now sleep.
Her world faded away.


[Continues...]

Link for part 2:
https://www.furaffinity.net/view/39078666/