In "Sister Is Jealous Coz I'm Perfect. Unlike HER," the protagonist enjoys a seemingly perfect life, excelling in academics, sports, and social situations. This perfection, however, breeds jealousy in her sister, who feels overshadowed and insecure in comparison.

As the story unfolds, the protagonist becomes aware of her sister's feelings, leading to tension between them. The sister’s jealousy manifests in various ways, creating conflicts and misunderstandings within their relationship. 

Ultimately, the protagonist learns the importance of empathy and understanding, realizing that her sister's struggles come from her own insecurities. The narrative explores themes of sibling rivalry, the pressure of perfection, and the value of supporting one another despite differences. In the end, the sisters find a way to communicate and appreciate each other's unique strengths, fostering a stronger bond.