It doesn't really matter where he comes from, so long as he has access to education and feels sufficiently dissatisfied.
d10 table of origins:
2 Emperor's brother (canon)
3 a Shugenja (possibly Master of Void)
4 probably not a gardener or a Unicorn, but sure why not
5 an Akodo daimyo
6 a Bharata monk
7 the vengeful leader of a massacred non-rokugani people
8 a Kholat Courtier
9 an Asako Henshin
0 a merchantReads a book by Kuni Nakanu on blood magic and learns how to use it from his bff Asahina Yajinden. Makes his fanboy Jama Suru do the actual blood magicking, so he and his bff can stay taint free. Supposedly goes globe-trotting through the desert with bff Yajinden, fanboy Suru, and wife Tsugiko, along with an entourage of Imperial guards that can't hack it and die.
Eventually convinces some Khadi to make him an undead servant by ripping his heart out and placing his LIFE FORCE in said heart, so anyone who holds the heart controls him and destroying the heart is the only way of killing him, then steals his heart back and runs off.
Don't have to include the road-trip, since it's gameplay irrelevant. Can just have him run into a Khadi in the Empire. Or you could skip the heart entirely and have him and his friends eat mermaid barbecue.
Considering both Yajinden and Suru become immortal (as well as Yajinden's apprentice Fushiki) and Tsugiko dies, you could have Iuchiban trying things out on other people while he searches for immortality. Tsugiko dies in a failed attempt, Suru succeeds but Iuchiban doesn't like the way it turned out, Yajinden is a success and Iuchiban follows up by performing the same ritual on himself.
Either way, he returns, founds the Bloodspeakers, raises a zombie army, big fight, the end.
Seeing how the bloodspeaker cult is the most game-relevant part of the sub-plot, I'd suggest they be an early product of his rise, a means of casting a wide net as he looks for ways to not die.
Early bloodspeaker factions:
- Heirs of Isawa, a group of Isawa-trained shugenja believing that the stigma on blood magic is largely arbitrary, arguing that Isawa himself was a skilled user of blood magic and that it was blood magic that defeated Fu Leng and sealed him in the black scrolls.
Iuchiban's wife, Doji Tsugiko, supposedly makes up for her lack of beauty and charm by being clever, yet canon Tsugiko uncritically believes everything Iuchiban tells her. It's clear that Iuchiban doesn't care for her, despite her devotion. Probably the Hermione of the group. The only one of the core four that never gets to be immortal.
- ideologue of the group, selling the bloodspeakers to the lesser fortunate as a true meritocracy in a rigged system
- the creepy fangirl to Jama Suru's creepy fanboy, using her Doji education to compose poetic shipping fanfics based on official histories and religion
- a Kuni shugenja, heir of Kuni Nakanu, and the one introducing Iuchiban to Nakanu's books
He's the one in the group with the most to prove, and will likely do a lot of things for no other reason than to boost his psychopath nihilist credibility. He can only possess willing vessels, but his disembodied immortality makes him a borderline deity in the bloodspeaker cult. The longer he possesses someone, the more they start to look like him.
I imagine him as a longtime fan somehow ending up a member of their favourite band.
The shugenja Asahina Yajinden considers himself an artist. He spends large amounts of time crafting really messed up magic items and is Iuchiban's blood magic study partner.
Famous Yajinden brand goods:
- Four bloodswords (see below)
- zombie-making masks made from porcelain
- extensive journals full of pseudo-philosophical ramblings on his life and beliefs and the nature of the taint (may or may not use zombie scribes to mass-produce his and Iuchiban's writings for the bloodspeakers)
Has an apprentice that he slaps a magic mask on and turns him physically dead/immortal and rotting, but with his mind intact. Said apprentice, the peasant Fushiki, smells strongly of both rotting flesh and the heavy perfume he's trying to hide the former with.
He regrows limbs and doesn't need air or food or water to survive. The only way to kill him is to destroy the (incredibly tough) mask on his face. He's the one major character of the sub-plot that would be sincerely grateful if you manage to kill him.
The bloodswords give us some feel for the behavior of certain important political figures, as they are all gifted to "Champions" of the time.
- Ambition is gifted to Bayushi Rikoji, who hides it, never uses it, and tries to figure out what is going on.
- Judgement is gifted to Hida Tenburo who murders his children in their sleep and commits suicide.
- Passion is gifted to Doji Tanaka who publicly confesses his love to an 11-year-old commoner and throws himself off a mountain. I used his ghost in a campaign once.
- Revenge is gifted to Akodo Meikuko, known as a calm and cool-headed general before she starts flipping out and killing people over imagined insults, possibly dying from an arrow overdose.
"When you hold that sword, all girls look 18"
- the Gaki of Doji Tanaka
The first rise ends with an immortal sorcerer leading an army of the dead from within the capital in an attempt to conquer and control the Empire, the cremation of the dead being made mandatory in the aftermath and the immortal sorcerer being chained in a tomb. Yajinden is brainwashed. The bloodspeaker subculture goes out of fashion. Nothing disappears.