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.
Kenshin and Sano were lovers before Saitou showed up… but Kenshin and Saitou liked each other long before that. One thing’s for certain, at least: Saitou and Sano hate each other. Right?
Having been slaves for most of their lives, they know that love is both a luxury and a weakness they can’t afford; with Sano obsessing over a guard and Katsu enchanted by a newly-arrived fellow slave, however, they may not be able to help themselves. But something bigger than that is going on around them, and their growing feelings may be the least of their problems.