Strange situations keep arising whenever Sano gets drunk. It’s easy enough for a curious Saitou to set up the right circumstances to learn what’s going on… but then he has to deal with what’s going on.
Why did Saitou kiss Sano on their way into Shishio’s fortress? Can Sano figure it out now Saitou is dead?
Before Sano confesses his love to Kenshin, he needs to get his attention and impress him, and therefore appeals to Saitou to teach him defense… but Saitou may teach him more than that.
Badly wounded after his escape from Shishio’s fortress, Saitou finds his life unexpectedly in Sano’s hands.
Regarding a one-night stand between Saitou and Sano, there’s some confusion that takes a little time to work out.