So tota is cheating on kirie? I get the feeling kuromarou might eventually end up a boy for the sake of being slightly physically stronger.
Cheating? She is not his girlfriend. Even if she was, kissing for a Pactio wouldn't really count as cheating. We'll see what happens in the chapter but last time the real issue was because he wasn't use to a female body. If he gets used to it I don't think he would care about a boost in physical strength, it's not that important anyway in this series.