Nachi Igarashi, a Japanese male with brown hair and brown eyes, shares his home with his brother Toshi and two interdimensional beings, Compiler and Assembler. These visitors originally intended to conquer Earth but abandoned their mission to reside in the human world. A growing romantic tension simmers between Nachi and Compiler, though neither openly acknowledges their feelings.

When the interdimensional council issues a three-day ultimatum for Compiler and Assembler to return—threatening Earth's destruction if they refuse—Nachi becomes entangled in defusing the crisis. Amid this looming peril, his unspoken connection with Compiler intensifies. The arrival of a mysterious assassin targeting interdimensional entities further complicates Nachi's struggle, forcing him to aid Compiler and Assembler in confronting this lethal new threat.

As one of the Igarashi brothers central to a narrative of interdimensional integration, Nachi's actions revolve around protecting Compiler, navigating their evolving relationship, and countering dangers from their home dimension.