The Princess and embodiment of envy.

Taking the form of a deep green sea creature based on her mythological counterpart the great serpent of the seas The Leviathan, while she has serpentine features she more resembles that of a bipedal lobster with hard carapace armour and a set of pincers, at first glance, Lyra is the most unique looking of the 7 princesses given her small size of 8ft comparable only to Lucy's human form of 7ft but more so for her defining features of the seaweed that is tied around her wrists, ankles and neck that are always floating upwards as if an ocean current is forcing them upwards, whether she is standing upright or laying down on a bed the seaweed always goes up, but in reality, it is not an ocean current but rather a gravitational pull, being pulled to a water drenched cross of driftwood that floats above her glowing green crown, the more astute putting 2 and 2 together and realizing the seaweed is the strings and the driftwood is the puppet cross.

This might seem odd for the ruler of a ring but when combined with her other defining features it will make sense, the 1st being a swirling green emerald embedded in her chest between her bust, with a motif of it being tied to her by old waterlogged rope, however, the rope is purely aesthetic, just something to wrap around herself to make it stand out more while the gem is the only thing that is fully embedded in her chest, with this gem being hard to the point that it is indestructible but it is also sensitive.
Lyra and all envy demons bear this swirling emerald fused into their chest and like most things here are cursed, radiating a low-level hypnotic aura that makes anyone near it look at demons of envy as a generic "background character", D-tier at best. no matter how hard you try and stand out or do amazing things, no matter what you accomplish you will never be noticed, but all others will be and you will see them get popular and surpass you in every way and unlike others like Darkness that willingly puts on a puppet suit and follows Midnight's orders to make her even richer and more popular its by choice and for a bit of fun as if they chose at any point they could use their void power to remove anyone and anything they see fit. this gem and its power on the other hand is by force, forced to fade into the background for the real main characters and it will make you jealous as they get everything you want for half the work, you work so much harder than them and your still nothing, a loser, a background character that will never be noticed because of the emerald's power with it also affecting you, only heightening your feelings of jealously and envy and no one knows that feeling more than the lobster queen of envy herself, a sin just as powerful as her sisters yet forced to be in the background to them, most of the time ignored by her sisters even if she has a point to make. When she finally is noticed all her bigger sisters will still treat her as the lowest of the 7, grabbing her cross for a fun forcing her to dance and act the fool for them as being a background character that's all your good for, there "Fun" setting her off and her gem only further fueling and heightening and of course, perpetuating her jealously and envy.

Envious of Mammon's riches & popstar popularity,
Envious of Azzy and her ability to indulge in any dark desire she pleases,

While Lyra can only indulge in 1 single pleasure and be turned on by one single thing, that being belittled and told she is a nobody while feeling the pull of her seaweed. putting her cross on a hook that either gives some resistance to her seaweed or forces her to outright dangle there from her cross to pleasure herself while saying things like.

"I am just a grunt" "Fade into the background" "My sisters are the real stars" "I'm happy being worthless and insignificant"

or having another one of her demons call her & say these things to her while being pleasured, all the while having an annoyed and angry look on her face, she hates everything she is saying but it is the only way she can "get wet" having no other choice with her gem forcing her to say such things and feel this way when looking for any kind of pleasure.
And it's not like she can escape it, no envy demon can as the gem in the chest is indestructible not even a Holy attack or even a Void attack can damage it, both can damage or destroy the body but not the stone itself, and this is even more so for Envy herself as not only is she bound to her unbreakable gem's curse but she is also bound to her seaweed and cross with both the seaweed and cross also being unbreakable and as a sin, she can't even be damaged by anything but her blessing counterpart & void entities and even then is questionable whether anything but high-level void entities like "The Light" or "The Architect" would even be able to damage her being that Lyra has the highest defence of all the 7 given her armour like shell and unbreakable cursed items.

But out of all of her sisters, the one she is the most envious of is her insect sister Bella,

Envious of her freedom, her freedom to detach from her egg sack and move as she sees fit while Lyra is controlled by her gem which being the original has a stronger hypnotic field than all others only making its power even worse and making her envious feelings even greater and of course her seaweed and cross that if one of her sisters' grabs can force her to move how they want and say what they want, even letting to cross control her via putting it on a hook to feel some kind of pleasure.
However this is not to say she is unloved, she knows her sisters love her and when they break through the aura of the gem and acknowledge her existence they do tell her how much they love her and appreciate her and how mentally she is the strongest of all the 7 having the mental fortitude to bear the gem of envy and the curse of ignored "D-plot" at best so every now and then she has a moment of happiness before returning to her ring and succumbing to her puppet cross and gem once more.
Now while all this might make her seem weak as she is small and a slave to her gem and seaweed and so on she is, in reality, the deadliest of all the sins even more so than Wrath, while Wrath ranks the highest as the 7th and final ring is filled with only the most violent and sadistic mother fuckers ending up there and Sindy herself unrivalled in combat ability and the 3 types of fighting aura, taking great pleasure in the suffering and pain of others, Lyra and the envy ring is 6th for a reason that is if Lyra or and envy demon ever has a violent outburst, due to the gem's power and making you fade into the background you will never know its coming or its was her, she could go on a rampage across the rings killing tens of thousands of demons and sinners and no one would ever know, all of them respawning on the edge of there respective rings calling bullshit on how they died as there was nothing around them, this even extends to machinery, Lucy once brought her sister to "The Factory" as a test with the cameras never once showing Lyra as she killed test subjects no matter how strong or smart Lucy made the camera, the ai and machinery overall, the power of the gem would always override it as being nothing but a generic background grunt even a machine that has no mind or emotion somehow treats you as a worthless background object so worthless that your not even worth showing or acknowledging on camera even though that is its one soul function and purpose to show things. Even the queen of all of Hell's powers creating perfect visual devices still made it just look as though workers were dropping dead for no reason, the closes she ever got was using a camera that had all of "The Factory's" power poured into it for a few minuets and even then with an entire rings power poured into it the most it could every capture was an extremely static "Deep Fried" 30 seconds of footage that was mostly unwatchable with the only thing you could make out in the pixelated 240p mess being a green blob moving and grey blobs falling.

So giving the Gem's power to make you become nothing more than a generic NPC that no one will notice or pay attention to demons of envy are extremely dangerous as there jealously drives then to try take things from others and they will never know its coming, of course this is only for normal sinners most arch demons or even stronger demons will at the very least know there is something there, but Lyra has the mother gem and all other gems mimic its power so hers is absolute and seeing her is almost impossible with only the Sins and a very select few arch demons with total mastery of there observation aura like Furia being able to break though the gems power enough to know she is there and of course void entities as there whole point is any and all powers and abilities are reduced to zero, all things become null and VOID, so the power of the void instantly negates the gems power, witch is why sometimes Lyra will ask Midnight if Darkness is around to visit as Darkness being a void entity, he is the only one that totally negates her gems power and can hang out with her without having to constantly focus just to try and see her allowing Lyra to have a real conversation or day out.

But to wrap the combat, we have a girl that cant be seen and is fuelled to kill because she is envious of you for one reason or another witch is already deadly in of itself but she has 4 actual combat features that set her above most when it comes to combat one being her aforementioned hardened shell that makes her pretty much immune to damage from a defence stance but offensively she being a lobster has her pincers with razor sharp jagged edges, these can slice though pretty much anything and can take most creatures heads clean off if she can open her pincer wide enough and even if its something thicker its still not going to end well with her being able to out put a crushing power of 100,000 PSI roughly enough to crush most high density metals with her maximum crushing power equating to that of a car compactor or deep water pressures that can crush lighter built submarines, of course she can control what PSI she outputs as not to harm someone she likes but if she is enraged and gets a hold of something its done either via razor sharp cutting power or immense crushing power.
But that is usually just the killing blow as before that she as her angler light on her head that emits low-level hypnosis like a real angler putting onlookers into a trans like state where they can't look away before striking them with her scorpion-like tail and stinger that injects a paralyzing venom into them making the victim unable to move for 24 hours you will be awake and know what's going or can fall sleep but your body won't be able to move at all, allowing her to do whatever she wants with you like in battle she will just walk up to you and snip your head off.
Wrapping up, Lyra dose have one special moment and key defining point about her ring, that being like her sister Mammon she to has had a interaction with "The Architect" upon learning about the fountain of creation and how it works that being once a creation is made all the waste water and ideas that did not make the cut are flushed away into the nothingness and it evaporates into "The Void" itself, upon learning of this and being what she is and how her gem and cross make her act a background character, a nameless grunt that fades into the background forced to be forgotten to keep her envious of others she got in contact with the "The Architect" asking if the run off can be re-routed to the envy ring all the ideas that never were all the BETA concepts that never made it rather than just becoming nothing send the waste water of the fountain to the envy ring as all these background elements and forgotten ideas fit her, witch after going back and forth "The Architect" agreed, talking a trip to the envy ring and placing a pipe at the very top centre of the envy ring, taking the molecular structure of Lyra's gem and applying it to the pipe to make it unbreakable, Lyra building her castle directly under it with the sewage flowing around her castle and into a toxic waste like lake that surrounds her castle, diverting it to different areas using channels within her castle to divert it to places she wants it to go a swimming pool, a fountain, her shower, a swimming pool of failure for a failure to swim in, a shower of failure for a failure to wash in, its all a d-tire grunt deserves and like with her pleasure problem showering in failure or swimming in it annoyers her but its fuels her gem and makes her envy stronger and makes her gemstone and cross's power all the stronger.