There is a h-manga I read really long ago. It's a school harem manga. There is only one thing I remember: there is a last chapter or an extra chapter where a girl rides a bike to meet a bikers' gang (around 100 bikers), and they have a gangbang. It's an extra chapter so she doesn't have any action with main mc, just bikers. One of biker calls that girl a giant slut as a joke.