Fuuka's sudden growth spurt catches everyone by surprise, especially her older brother. What was once an adorable childhood crush has morphed into something far more awkward now that she's developed into a young woman. Her classmates don't help matters, nicknaming her "Saipu" after the mythical cyclops because of her long bangs covering one eye. The real problem is that Fuuka takes her childhood promise to marry her brother completely seriously, determined to make good on a vow she made years ago when the idea seemed innocent and cute. Caught between wanting to be treated like an adult and still acting like an impulsive middle schooler, Fuuka barrels through daily life with relentless energy. Her brother desperately tries to establish appropriate boundaries while she refuses to accept his rejection. School, family dynamics, and her own confused feelings about growing up collide in absurd, comedic situations. The show finds humor in the collision between childhood nostalgia and adolescent reality, where Fuuka's brazen confidence constantly puts those around her in uncomfortable positions.