InuYasha: Volume 48

by Rumiko Takahashi, 186 pages
Sesshomaru learns to wield his inherited magical blade with a merciful heart while InuYasha and company fend off an emotion-consuming demon and then battle one of the presently discommoded Naraku's proxies.
When Sesshomaru's normally stony face suddenly starts revealing what he's feeling, you pay attention. Over the course of the series, creator Takahashi has here and there shown him making a sweetly irrational decision (almost always involving little Rin) which he unflinchingly explains away as perfectly rational, but she goes 40-some books before she lets something hit him so hard it makes him utterly forget himself. It makes for some effective (and affective) characterization.