The premise of the manga was that Hori's parents were never home, so she had to take care of her brother.I always wondering what is Kyosuke's job
This is why the chapters that introduced it were titled 'Gap' and 'Gap: Part 2'... people just decided to infer that it was just straight up masochism and not think any further.I'd like to think that it's not necessarily masochism on Hori's part but rather a kind of "Gap moe".