The title should be "a little sister can't accept her loss," page one "let's play a game together," page three should be "I win," page 4 should be "my brother is a noob."
Everything made sense though, thanks for your work.
The Japanese version of sadist/masochist seems much less extreme, "likes teasing" vs "likes being teased" describes it well. You'll see fairly vanilla manga mention it, or slightly raunchy interviews ask "are you an S or an M?"