Katsu is a 24-year-old guy who is an imaginary friend created by a teenage girl many years ago. Imaginary friends don't age, so he looks the same as before. He has a lot of piercings and several tattoos. Calm, relaxed, unflappable, carefree. He wouldn't mind making a deal with a man and becoming his friend, but still it's not his life's purpose, and he's happy to live there. None of the people except the "friends" can see him or the others outside the "house".