"Milena is an exotic individual, her existence itself violates a lot of rules, both natural and institucional,her biography is not long since she is quite young, but still quite interesting,she is a biomodified being created by Eva, the chief doctor in Danadriel's flagship, Eva modified an naga egg before hatching using nightmare era biomachines, ethically questionable to say the least, if was not by the influence of Danadriel she would end up in a bonfire for it.
Eva worked on her secret pet project for almost 7 years, polishing flaws modifying traits and adding benefits for her creation, her objective was to create an naga variant that was friendly and useful to the mammalian people, she removed the toxin glands, made the skin smoother, added eyelids and a frindlier face more similar to mammals, but most importantly and the most time consuming part of the project was modifiying the brain to allow the snake creature to feel empathy,Once Danadriel discovered the project he punished Eva with long and grueling penitence sessions, but he did not destroyed the egg, even being a hardline religious leader he was quite curious to see the final results.
Moments after hatching Milena showed that she was definitely a different creature, she craved for maternal love like a mammal baby, she grew fast, being able to speak fluently only with 3 years, she learned how to read at 4 and was a capable and mature as a regular adult around the age of 7, so far so good her development have no major problem, the real issue came as she grew more, by the age of 16 she reached a towering size and her hunger was imense, she only require food 3 times a week but the meals would neeed to be big, normal food wouldn't be enough, she required to eat whole creatures to be satiated,in normal circumstances that would be the end of the experiment, but Danadriel in his somewhat sadistic mind found a solution for the problem, simply giving living prisoners for Milena to eat, she protested at first, but accept when they agreed to give her only the nastiest of pirates and criminals,some of airship crewman claims that Danadriel likes to watch Milena eating the living prisoners, they swear that he rejoices in pleasure watching their slow and degrading demise.
With the passing of time she became a quite religious and spiritual person trough her readings, an inevitable consequence of being raised in a flying monastery, she understood the holiness of mammal beings and why the reptilian kinds were shuned according to the holy texts ,then it evolved in to self hatred and a spiral of depression, she concluded that her existence was a waste and the experiment a failure, no matter how much modified her body was and how pleasant was her behavior, she was still a monster, her species is naturaly destructive and nothing could change it with this conclusion she begged her creator to destroy her,Eva is a cold and stoic doctor, but even she could not simply end the life of her most beloved creation, having no way to convince Milena to stay alive she asked Danadriel to put an end to the sufering of her creation...
Danadriel agreed to execute Milena, he loaded his hand cannon and put it against her forehead, her only last wish was to be able to pray in loud voice one more time, he granted and paid atention to every single word of her final pray, then he lowered his weapon and asked her again, why she desired to die?and she replied with "because I'm a monster my lord" and he almost joyfully replied to her:
" Yes you are, and so I am! I tower over mortal man, the ground trembles as I walk, even the most dangerous of criminals only whispers my name in fear, I gorge in the blood of innocent folk and I bath in the gore of battle! but thats no reason to end our lives for we are monsters with a holy purpose! Omaro gave me a mission in this world, his pale light is my beacon in the eternal night...and as it seems his light has touched your heart, even being an abominable creature in flesh you was able to accept his word...and in his teachings you may find a reason to live...and even better a reason to fight!"
These words opened Milena's mind in a way she could not foresee, she understood that she would not achieve anything denying her nature or hating her existence, she had embrace what makes her a monster and use it to her advantage, use it for a holy purpose!after it she focused the next months learning how to fight, and how to use her monstrous body to cause harm to those who oppose order and the word of Omaro, there's no fighting manual for snakes, but Danadriel had alot of experience fighting nagas, so he told her all the dirty tricks her species could use,didn't take long for a conflict appear on land, a small anarch revolt, nothing to write home about, but a violent engagement anyway, she deployed with few other unities, she did her best, she used every trick on her sleeve, firearms, stealth, venon, brutal melee atacks and even crushing with her tail, in the end she was exausted and wounded but absolutely proud of herself!since this she participated in a considerable number of missions , specially the ones who require stealth and subterfuge, and some of kidnapping since a snake belly is really useful to transport living beings." (The traveler )

yes I got inspired by that new Xcom XD

If you are wondering how a giant snake can be stealth in broad daylight, simple, nagas are supernatural creatures, they can passively distort the mind of the observer, she is only seem in her real form if she wants to, otherwise you will see a completly random person in her place, the downside of this power is that it only works with weak minds , other supernatural creatures like vampires or werewolves can see trough the ilusion.

for those who are unaware of her difference to other nagas, basically they are utterly hostile to any other form of intelligent life, they dont care for anything but themselves, they contamine the soil and water they touch with their toxins, what they dont kill immedialy they torture for ritualistic purposes, the mammals aren't simply bigoted agaisnt them, these things are fucking awful and deserve to die. :U