Kyukyu emerges as one of two angels awakened when twin princesses Fine and Rein touch the legendary Soleil Bell at the Royal Wonder Academy, granting the sisters the title of Universal Princesses alongside Pyupyu. These angels serve as steadfast companions and aides to the twins, supporting their mission to combat threats from an evil force tied to the Black Crystal Planet.

Confiscated by the academy's head teacher for violating rules forbidding friendships, Kyukyu and Pyupyu remain intrinsically linked to Fine and Rein. Their mischievous antics persistently disrupt academy affairs—interfering in classes to risk point deductions for the twins and unleashing chaos in the town that demands the princesses' intervention.

A defining conflict arises when Pyupyu shatters medicine obtained by Fine, igniting a quarrel that culminates in Pyupyu fleeing home, revealing Kyukyu's role in stoking group tensions. Both angels later draw the attention of a "Prince of Darkness" figure, spurring rescue operations by the twins.

Despite ongoing challenges, Kyukyu and Pyupyu integrate into the academy's social fabric, notably celebrating a half-birthday event. Their actions consistently propel plot developments central to the twins' endeavors to nurture friendship and thwart antagonistic forces at the academy.