Youruichi is so underrated here. not even on some lists
1. Byakuya (Liked his conflict with rukia and his emotionless, rules over all else type attitude)
2. Youruichi (She served as a good mentor figure, just generally liked her design and role in the soul society arc)
3. soi fon (Found her romantic obessesion over youruichi-same, to be interesting)
4 Muramusa (Liked how his power uses the abilities of the heroes against them)
5. aizen (cause his monologue about how people deny facts for their own perceived truths, Is something that is quite true and understandable to me)