Yusuke Kamoshida begins the series living alone until he discovers a naked girl named Noelle in a forest. This encounter abruptly transforms his solitary existence when Noelle's entire family relocates into his home, replacing it with a large plastic-like castle. Forced to adapt to their chaotic household, he struggles to maintain external normalcy by concealing his bizarre living situation while attempting to contain internal disorder.

Initially, Yusuke harbors a strong crush on his athletic classmate Natsumi Suzuhara, often watching her diving practices with friends Saiki and Masaru. His ability to observe Natsumi dwindles as Noelle's energetic antics demand constant attention. Natsumi initially views him as a pervert due to misunderstandings stemming from Noelle's actions, though her attitude later softens into tentative attraction. Yusuke's lingering feelings for Natsumi clash with his resistance to Noelle's immediate and persistent affection.

Passive by nature, Yusuke rarely asserts himself against the whims of Noelle's monstrous family. He frequently embodies the "Only Sane Man" trope, serving as a grounded counterpoint to the eccentric cast. Parallels to Shinji Ikari highlight shared traits like timidity and parental issues. Despite exasperation over Noelle's disruptions, he consistently rescues her from trouble. Her Frankenstein-like father routinely calls him "son-in-law," reinforcing familial expectations.

Yusuke's character evolves significantly across the series. He initially rejects Noelle's marriage proposals after her transformation into an angel and clings to his affection for Natsumi. Gradually, his feelings shift, culminating in him reciprocating Noelle's love by the conclusion. This journey from reluctance to acceptance solidifies them as an official couple, defining his arc as he embraces his chaotic life with Noelle and her family.