Admin Mawile: (ゝω・)ノI assume you mean Yui herself, not the reader?
-Reiji, in anything sexual, has to have control. He’s far too afraid of losing any shred of dignity to ever give up his position as a commanding dominant, and Yui is more or less forced to go along with what he wants. Reiji is the definition of manipulative, and winds up half convincing Yui that what he does is what she wants/deserves in the first place, and Yui winds up caught in a dangerous loop of trying to satisfy someone who’s toying with her.
-However, the more he loves Yui, the more fairly Reiji treats her. He’s capable of being kind when he tries, and once Yui has become someone that he can’t live without, he’s much more willing to be gentle with her. He goes from using her as a plaything meant for nothing more than entertainment and manipulation, to treating her as something of a genuine partner. In the end, while still rather sadistic, he’s not an entirely bad lover.