Taiki is Nakatsu's roommate and best known for his ESP abilities—he can see ghosts and read auras, which he's constantly analyzing for Nakatsu. He's also pretty into yoga. When he first transferred to Osaka High, other students gave him a hard time because of his supernatural skills, but Nakatsu's always had his back and treats him as a genuine friend.
There's some neat trivia about his name: Nakajo revealed in volume 4 that "Kayashima" comes from Kayashima Station on the Keihan Main Line. Apparently the station's construction was rough—several workers got hurt trying to fell a large tree on the site. Instead of removing it, they ended up preserving the tree and building the station around it. The kanji for "Taiki" literally means "large tree," which is a pretty clever connection to the station's history.
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