A hamster girl falls in love with her oniichan.
Unable to confess, Umaru Doma is gifted by a deus ex machina with the boy's other phone number. Never minding the strange area code, she immediately calls Taihei Doma, and is overjoyed to find out that he has a crush on her as well.
But, the next day, when she recounts the previous day's confessions to her oniichan, he only looks at her with a perplexed expression on his bespectacled face. After some investigation, she finds out that the big bro she called is not the same big bro she fell in love with. In fact, this Taihei doesn't exist in this universe at all. He is the alternate universe counterpart of her crush, who has fallen in love with his sister as well, who too is blissfully unaware of his crush.
Hijinks ensue as they strike up a deal to give each other their darkest, most private secrets in order to equip each other with the weapons they need to conquer the heart of their other selves. While the two chase their respective loved ones, DRAMA ensues as they begin to fall in love with each other instead and question the NATURE of CORA and JUMPU.