It could also be an internal identifier used by a company or a group. Maybe it's related to a game or a fictional universe that is not associated with adult themes. For instance, it could be a level or an area in a science - fiction based game.
The characters can be integrated by having them meet in a crossover world. For example, Naruto characters could be transported to the Claymore world and vice versa. They could then exchange their fighting techniques. Naruto characters could teach the Claymores about chakra control, while Claymores could show Naruto characters how to use their yoki - enhanced weapons.