So we still don't know Ogata's true motives with respect to the Ainu gold, right? Him killing his half-brother and father were for personal reasons that just happened to coincide with Tsurumi's goals, though I think that's been clear for a while. He also saw through Tsurumi's schemes unlike the others, so he had no reason to stay with the 7th division- Usami was just projecting when he hypothesized that Ogata felt betrayed by Tsurumi after treating him like a father-figure. He probably sees Hijikata's group as an ends to a mean rather than as allies, but I still don't know what his endgame goal is.