Half a century ago, Earth faced annihilation at the hands of the Cosmic Demon Delekacon. The creature was sealed away just in time, but its severed left eye survived. That eye, named Pec, has been living quietly on Earth ever since, spending his days as a permanent freeloader in the home of his best friend, the young man Keigo Torase. Pec appears as a small, humanoid figure and goes by the nickname Eye Boy. He has no interest in his demonic origins and is perfectly content with his lazy, ordinary life.

The peace is disrupted when Delekacon's right eye also arrives on Earth, signaling that the sealed demon may not be as dormant as everyone believed. Pec must confront whether his carefree lifestyle can continue or if he will have to face the legacy of the Cosmic Demon. The story is set in a contemporary Japanese town, blending everyday youth comedy with sci-fi and supernatural elements. The core relationship is the odd-couple friendship between Pec, the demonic freeloader who just wants to play video games and eat snacks, and Keigo, the human who tolerates his antics. The main narrative arc follows Pec's reluctant movement from total apathy toward a decision about his own future and the safety of his friend, culminating in a confrontation with the other half of the demon that once nearly destroyed the world.