any backstory as to why he feels this way toward the nobility/c46? if your character is mainly driven by a desire for personal power, supporting the abolition of the current government is a very dangerous game to play, especially without friends. why doesn't he want to work within the current power structure? maybe he feels stuck, got in a spat with the nobility that kind of dead-ended his career? i think having that idea (overthrowing everything) coming to your character in game (versus having it preset) would be super fun to flesh out and also end up making you much more dangerous when raghnall finally realizes that's what he wants.
Yeah, I think having the finer details of what he wants come about during the actual story would probably be better. At the start he'd have desires to change things but no real idea of what should change or how. Bit of an info dump, but heres a good amount of backstory that I wrote up to explain why he hates the nobility. Hopefully it should make a bit more sense to anyone reading.
Dying sometime pre-1200 A.D., Raghnall found himself adopted into and living a life of near-luxury among one of the richest families in the upper districts of the Rukongai. Despite them being quite well-off for Rukongai citizens, the amount of food they could afford or the nice things they could buy were still limited. Both they and he wanted more, perhaps even needed
more given Raghnall's latent potential. Ever since first arriving, he'd always been jealous of the greater lives that the nobles within and without the Seireitei led.
As his jealously festered, the rumblings of a catastrophe in the Human World grew louder. The growing Mongolian Empire craved more and more, led by violent warlords such as Genghis, Kublai, and Timur. As the sheer toll of deaths caused by the wars, massacres, and disease piled higher, vast swathes of needy souls flooded into the Rukongai. By the end of the conquests, more than 30 million people had died on Earth.
With so many new souls to house and feed, even the richest districts began to strain under the weight of all of it. As the balance of souls slipped further, those black-and-white devils within the great walls began to venture into the Rukongai. Desperate to maintain the balance, they killed an uncountable number of residents. At first Raghnall agreed with them - after all, fewer hungry mouths in his district meant a better life for him. But his tune soon changed when his own began to be culled. When his own family and friends died, it was no longer the valiant Shinigami merely doing their job - it was the dogs of the Nobles slaughtering innocents. While they lived comfortably in their mansions, never needing to welcome hungry newcomers into their homes, millions poured into the Rukongai and millions were executed.
Resentment grew within him as he begun to blame the nobles more and more for the ills that beset the Rukongai. Soon he found himself associating with roaming gangs of souls who would seek out low nobility or even those distantly related to them, then beat them within an inch of their life - sometimes past that line. Yet violence and direct conflict were not in Raghnall's nature, so he soon found himself acting as a planner for the group. He would investigate and track anyone that their outfit did not trust or like. Of course, this would not last forever - the Shinigami soon realized what was happening and sent their men to crack down on them.
In the midst of the night as Raghnall and others poured over accumulated documents, one such Shinigami burst into their meeting. They proceeded to cut down one conspirator attempted to arrest the others. Raghnall clung to the wall in the back of the room, eyes wide as the blood of his fellows soaked into the floorboards. An accoutrement hanging from the man's robes caught the moonlight, exposing his noble status. Something within Raghnall snapped, the thin rope of his restraint gnawed away by years of hatred. Gripping a sword he did not have from the scabbard of his twisted soul, he struck out and opened the man's back to the moon's gaze.
Those who had witnessed the events had no wish to speak of it. With this newfound power, Raghnall did the only thing that made sense to him. Seeking to infiltrate the Gotei and change the Soul Society from within, he joined the academy.
From there on out, he'd complete the Academy and get moved through some of the Divisions as is the standard. Since I've changed up his timeline a bit, he should probably be promoted more quickly as a direct result of the Black Death crisis. (The Mongolian conquests didn't end until a bit after we'll be starting, so he won't have been a Shinigami for too long.)
I'd leave the reasons for his wanting specifically the abolition of the Nobility and C46 to the early stages of the game. Perhaps one of the other characters, or an NPC such as his or another Captain, can act as a check on his progression through the ranks and open him up to the idea of further radicalization and lead him down the aforementioned path.
Again, sorry for the wall of text. Got pretty into it.
P.S. While what I've might imply he's doing all this for a fairly "good" reason, even if his actions are pretty fucked, he also does seek power for power's sake as well. The idea is for him to be Machiavellian yet closer to an ultimately misguided and selfish fool. But I'm not going to go back and add MORE to that thick block, so just keep that in mind.
P.P.S. - He hates Earth, and being sent there, with a passion. He finds it dirty and disgusting; the fact that those in the nobility as well others in positions of privilege (Hazuki Tsukimiya) do not get sent there (as often) is certainly something that fuels his loathing.