Takakura Ken is a boy who got cursed by the "Turbo Grandma" ghost. The only way to relieve the curse is by luring the ghost out of her comfort area through some kind of a race.
Takakura believes in UFOs and made a bet with Ayase (who believes in ghosts but not UFOs) to see whether UFOs or ghosts are the ones that are real.
Takakura was nicknamed "Okarun" by Ayase because the name "Takakura Ken" is the same name as her favorite actor.