Susume is a super M who prefers no-strings-attached relationships and Momo is his neighbour and childhood friend who is willing to do anything to be with him.
The age gap isn't weird. But the fact that Susume watched Momo grow up is definitely uncomfortable. Susume should have tried to push him away more.
Overall, it would be a hot and interesting story, otherwise. 4.4
Osanajimi ga Do M de Tsundere Nan Desu ga