Etsuko

The concept for her world is that they are Miko Gladiators. If you kill a monster with your spiritual powers you get a mark on your skin and that mark spreads and spreads the more you do. See references.

You also progress through the gladiator ranks.

But Etsuko herself encounters monsters outside of miko school and realizes they’re not so evil. She has to determine what to do and realizes that the oldest Miko who has killed the most isnt quite sane nor spiritual anymore. As a direct result of it?