Mint Chocolate Vol. 3 (manga)
I haven't been myself since the moment I fell for you...!
A Christmas confession leaves Nanami and Kyouhei at...well, Nanami's not quite sure. After all, Kyouhei kind of admitted that he liked her, and maybe even kissed her, but...then acts like his usual self the next day?! On top of that, someone starts spreading rumors about their relationship as siblings...which means even if they are actually dating, they can't tell anyone about it...!!