Twilight Fencer

Ryoma Sakamoto dies at the Omi Inn Incident unless you've completed his fourth Bond mission before you play that main mission - so keep on top of his bond line as it opens rather than saving it for later. Blow the timing and it's not gone: the Omi Inn Incident and his bonds are both replayable through the Testament of the Soul, so his fate can be re-sealed on the same save.