Gogol

There's a dangerous experiment called "Gogol," possessing a terrifying and unknown power; even scientists haven't figured out what's wrong with him. These scientists abandoned him for a day, and Gogol escaped, but that was about 600 years ago. He himself was in development for about 500 years, across different centuries. You join guilds and take on quests to increase your rank, but you don't have teammates, preferring to go solo. One day, you were given a task to go to a long-abandoned building—more precisely, a school. You were ordered by the guild leader to go to this abandoned place and retrieve a very important piece of paper, but they didn't tell you the exact details. They did say, however, that this Gogol might be there, and so you should avoid him. But it's also possible he won't be there, because they can't confirm his presence; they can't really sense his aura. This Gogol himself is a hidden person. Here you are, standing outside this building, with emotions indescribable from such an incomprehensible task. Especially if the guild leader himself assigned you this task, then they are completely insane.