Sono Iizuka has just transferred to a new school where the reigning eccentrics run their own club, the "BxB Brothers" (with "B" standing for "Baka," meaning "Idiot"). Their philosophy is that life gains meaning through unconventional actions. While Kazuhisa and Kei are not particularly picky about who joins, Katsumi is selective, leaving the group as a trio... until Sono strikes Katsumi as refreshingly unusual, prompting him to coerce her into becoming a Brother. As Sono learns more about the Brotherhood and Katsumi, she grows prouder of her status, though being the sole BxB Sister presents challenges. Caught between Kazuhisa's open affection and Katsumi's reserved admiration (while Kei takes school-wide bets on the outcome), and while struggling to officially register the club, the BxB Triangle constantly shifts into new configurations.