Introducing Cupid. There's only one, of course. At the start of the game, he must pick 2 people (he can also pick himself) who will be bound by eternal love (I'm sure you're all open to this). Essentially, this means that if one of the two dies, the other will immediately commit suicide and die too. These 2, of course, know that from each other, and it's their job to protect each other. Yes, it might or might not be hard, depending on your roles (roles that Cupid doesn't know about, of course). If the whole village dies, except for these two, they win (no matter what their roles are).
After Cupid has picked his two persons, he becomes a normal Villager. He doesn't do anything special after that