A sullen, unattractive slacker who's a childhood friend, next-door neighbour and former rival of Nana, Kaoru has been nursing a crush on her for an unspecified time before the start of the story. He used to be on par with her without trying until middle school, when her hard work and dedication to a goal began to pay off, leaving him struggling to catch up. As a result, he stopped trying and resigned himself to watching and urging Nana on from afar. He discovered BDSM around the same time.