Zhen Kaixin, called Kai Xin, is Shi Fen’s loyal partner-in-mischief, matching his friend’s reckless energy with equal enthusiasm for chaotic antics. His good-hearted nature surfaces unexpectedly, like when he covers Shi Miao’s cafeteria debts, unintentionally igniting her crush. A basketball standout at their shared high school, Kai Xin’s athletic charm and easygoing smile win peers over, though his guileless optimism often traps him in trouble—whether blindly abetting Shi Fen’s wild plans or misreading Shi Miao’s flustered hints.

His collaborations with the siblings spin into absurdity, like disguising as Shi Fen’s girlfriend to scam buffet discounts, a stunt that lands them both permanent bans. When tensions flare between the siblings over Shi Miao’s feelings, Kai Xin’s bumbling mediation amplifies the chaos instead of calming it. Yet beneath the clownish exterior lies genuine loyalty: he listens to Shi Fen’s fears for Shi Miao’s safety or lightens moods with goofy pranks, anchoring their group’s camaraderie against life’s turbulence. His blend of blundering humor and quiet dependability makes him the glue holding their unpredictable world together.