In the world of professional assassins, in order to get ahead of the game sometimes you've got to do something drastic.
Take Masane, for example. In order to elevate herself to S++ rank, she made a pact with a demon, then cut her own left eye out so that it could be replaced. The demon granted her vision of infinity, allowing her to see her target in her mind's eye no matter where they are or what they're doing... and of course, she gained powers to help eliminate them more discreetly, as well.
More to come.