Ken Takakura got stuck with a curse from the "Turbo Grandma" ghost, and the only way to break it is to drag her out somewhere unfamiliar and race her. Yeah, it's as weird as it sounds.
He's pretty into UFOs—like, genuinely believes in them. Ayase, on the other hand, is all about ghosts but thinks UFOs are nonsense. They made a whole bet out of it to settle which one's actually real, which obviously kickstarted their whole thing together.
Ayase calls him "Okarun" because his real name, Takakura Ken, happens to be the same as some actor she's into. He got stuck with the nickname and it basically stuck for good.
Content compiled by AnimeList.moe from publicly available sources.
