Lenn

Lenn's true identity is that of Princess Aliaentha Luxia, the second princess of Yuelin, thought to have died in the Areshia Academy fire five years prior.

He was born with undeveloped magic circuits, severely limiting his aura potential and ability. Because of this, and because the King preferred her elder sister and because there only needed to be one heir, Alina was raised not to be a ruler, but to be his sister's loyal servant and sword, living in the shadows to eliminate all those who threatened her. Even so, from a young age he far preferred to spar with the guards and ditch his etiquette lessons. He'd challenge the norms of femininity as well, showing up to training sessions in nothing but a tank top and pants — an outfit that he was scolded for for being "too boyish". The next time he showed up was in one of his fanciest dresses, one he tore straight down the middle in front of his teacher and father, and tied up into a set of makeshift "pants".  

As he grew up, he was subjected to harsher and harsher training regimes. He was thrown into the nearby forest at age nine, told to "find herself a partner, or die alone in the forest". He met a snivy, and saved her from a hungry liepard. Since then, the two of them have been inseparable. The two managed to make their way back to the castle after six days. Because of his father's only concerns that he grew up to be a valuable tool to the family, and his mother's distant aloofness and obvious preference for his sister, he grew up with nothing but Giwira and books to keep him company. His family outfitted him with the best equipment: mythril armor, a mythril-mesh assassin's suit, and a mythril-plated dress, as well as a mythril-titanium sword, all custom forged for him.

As harsh as his childhood was it did quite positively shape his abilities growing up. He achieved a perfect link with Giwira at age 15, perfected mega-evolution at age 16, and was able to utilize dual-link shift at age 17. He never lived at the academy unlike the other students, however he did manage to make a few close friends, namely, his distant cousin Tsumiyuna, Kamui, a draukyrn attending the academy on scholarship, Aidryn, a non-binary person who first made him realize his genderfluidity, and Hayate, the eccentric heir to one of the fae clans.

Unfortunately, the destruction of Areshia Academy and his supposed "death" meant that he was no longer able to continue his formal education, and never quite perfected dual shifting, though the years following brought on much self-tuition and growth. Regardless, he never developed the aura capacity and capabilities to truly use magic. He's capable of using psychic magic, as it relates only to manipulating outside auras and auras within himself, and a few augmenting abilities he picked up off his friends. He also studied healing magic and charms and seals, however he's unable to use both because of his lack of ability to project his own aura. Quite a nerd about magical theory, actually, and is quick to understand how (theoretically) to do something after observing it only once or twice.
He took to the streets after his supposed death (actually almost getting disowned but he renounced his family name and status as heir before his father could disown him), living under a myriad of different names. Some recurring ones are Thea, Kei, Chi, and Wren. He lived nearly exclusively off stealing and money made from fighting in the Underworld fighting rings; he didn't have the face to busk, nor wanted to take chances at being discovered by taking legitimate jobs.

That didn't last long; not months later, he was drugged and kidnapped by an unknown group, having most likely noticed him from his stellar performance in the fighting rings. He was kept with many other children, of which he noticed most were girls, with high magical potential and much younger than him. (Why was he targeted? The first condition fit, but he shared no other similarities, and could be easily identified as a difficult target?) They were not particularly being harmed much, other than being kept constantly drugged to docility. Regardless, the kidnappers likely didn't expect to need to deal with an assassin, trained from youth to have superior drug and poison resistance. In the time he spent captive, he befriended a few of the kids, namely Griselda, a songstress-in-training from the northern plains. Despite the semi-conscious haze the kidnappers tried to keep everyone in, he found comfort in the tunes she'd sing or hum as much as she was lucid. Two weeks later, he managed to instigate a mass prison-break, fighting his way out literally by tooth and nail. For the first time in his life, he used magic extensively, burning through what magic circuits should have been there, but existed only as a shadow of what others' were. For the first time in his life, he had people to protect— and failed. And for the first time in his life, Lenn killed.

Badly injured from the escape attempt, he remembered nothing between leaving the kidnappers' keep to waking up in a stranger's house, four days later. Nothing, but an overwhelming guilt that he had failed in something, something that held great importance to him, but was now gone. His savior was Azura— as in Azura Sianna, an aunt of many generations past. The current Guardian of Arceus, and the one who had caused the schism of the Aegis clan. Azura explained that he had nearly died — would have died, had she not intervened. The magical damage he had caused to his own systems was exacerbating his injuries— and preventing her from healing him at all. She'd saved his life by connecting him to her own eternity core, making him quite literally a dead man walking.

She offered him two options— either form a contract with Arceus, who can repair his destroyed body, or live like this — bedridden — forever, as she would not let the only living person capable of inheriting Arceus's contract die. Really, it was only one option, that he had to accept the contract sooner or later.

He accepts the contract immediately— the effects do not take in full effect until he next dies, allowing all the changes to set in. Over the next several months, Azura and Arceus both serve as his mentors. He finally chooses to fully discard his female persona, now taking the name Lenn, and Azura's last name: Sianna. Even though he had never been formally adopted, Azura was more of a parent to him than either of his birth parents.

Their time together would be cut short, however. Having secured an heir, Azura reveals there is a thing all Guardians of Arceus must do eventually— sacrifice their life and soul to become part of the leyline that cycles aura through the region. The reason the region's natural aura was disappearing, and why newer generations were losing many of their abilities, was because her predecessor did not do this, and for two hundred years, the mantle of Guardian was never passed down. But be it foul luck or fate, the two would never make it to the Origin Temple, where the rite was to be held. Along the way, they were attacked by Team Shadow, who had some way to disable or bypass Azura's immortality, killing her as she took an attack intended for Lenn. In her final breaths, she sent Lenn back to their home, where the wards built over centuries would ensure nothing could harm him.

With Azura gone, he turned back to his old ways, fighting and killing for a living. He was invited to the Assassin's Guild by the leader, whom he only knew by his codename: Bloodblind. In the guild, he proved himself to be worth far more than he appeared to, quickly rising through the ranks to be deemed the most dangerous of them all. His ability was in part honed from a decade's worth of training, and in part abilities gained from being Arceus's Guardian. Enhanced strength, speed, access to an eternity's worth of knowledge, Arceus's aura reserves as part of its divinity core, and most importantly, his magic circuits repaired. More than repaired even; while it would never be on the level of normal people, it was roughly patched enough for him to use magic without nearly killing himself at the slightest use.

In the years following he would even be approached by Team Shadow, offering him hits that they did not want to be associated with. As far as he was aware, never again did they actively try to kill him again, and wariness was slowly replaced by spite and vengeance for his mentor. He started mentoring two kids of his own— Frey Gallaghan, a kid from the slums, and Mason Grey, one of the children the Assassin's Guild leader personally brought into the guild as an apprentice. Both wound up going their separate ways, Frey studying at Agris Academy, and Mason joining Team Shadow.

Eventually he cut ties with the guild, building his own territory at one of the "gates" to the Underworld, Galen Bronwell's tavern. Though it was never explicitly stated to be his, and gates were supposed to be a no-violence, neutral territory, because he frequented the place so often, and truly enforced those rules rather than let thinly veiled hostility slide, the place therefore became "his territory".  

When the Aura Guardians arrive in Agris City, he reluctantly ends up helping them from the shadows, as they were his friends in his old life. Still, he tries to avoid them as much as possible, for the reason that he doesn't want them to learn of his old identity— that person was dead, as far as he was concerned. Lenn was no longer Alina, but a part of him still feared being judged by his friends, because he became the very thing they were supposed to fight against.

He's not afraid of death; he knows that revealing himself to the Aura Guardians means certain death for a criminal of his status— even though he cannot die, not as an immortal. But between revealing himself to protect his friends, when their base was raided by Team Shadow, and ignoring it and walking free, there was no choice to be made at all.