Hmm, much as a loathe dark backgrounds for their clichéness, here's my current thoughts:

Since we have a shrine maiden, a leader, and a warrior, I was thinking of filling the role of the ninja/support. 

Basic background I'm forming:

From a long line of ninjas in service to their lord, and one of the best of this dying art. Naturally when his daughter was born he began training her too to serve his lord in place of himself after his death. Eventually though, conflict brewed between his Shogun and one of the four Daimyō. He and his daughter undertook a mission to assassinate the Daimyō, failed, and she was killed in the process. Disgraced and disillusioned he changed his name and lived life as a bandit, already considering himself dishonored beyond redemption. Likely he ends up imprisoned because he wanted to be caught, but as for why he decided to escape afterwards... Who knows?

I plan to play him as more of an uptight deadpan snarker than a depressing moody stone wall. Mid to late thirties, fathered a daughter when he was eighteen, she died a teenager a couple years before the RP starts.