[O157] Ane to Sex suru Saiteki na Houhou

A couple of bullies shows MC's older sister a pic of male MC in a compromising position, and threatens to spread it around the school if she didn't comply with their requests. First, she's asked to strip naked, then asked to watch her take care of her brother's boner. MC acts all confused and guilty, but sister reassures him and they have sex. Afterwards, the bullies hop in for sloppy seconds and thirds. While this is going on, it's revealed that the MC was the mastermind where the bullies were just willing participants, where he wanted to create a situation where having sex with his sister would be justifiable and wouldn't be as weird. story ends with MC looking forward to banging her after everyone else has had their share.

I need context