A Galaxy Next Door follows Ichirou Kuga, a young shoujo manga artist struggling to keep his life together after his father's untimely death leaves him responsible for his two younger siblings. To support the household, he rents out rooms in the apartment complex he inherited and pours himself into his manga work, even as sales stay low, assistants leave, and deadlines close in from every side.
Just when the pressure becomes overwhelming, Ichirou is rescued by Shiori Goshiki, an extremely capable novice artist who becomes his new assistant. Her help gives him a chance to steady his work, but a bizarre accident soon leads to a supernatural encounter between the two, and Shiori unexpectedly declares them engaged. What begins as a strange interruption to his routine quickly transforms everyday life into something far more complicated.
As Ichirou tries to understand his peculiar relationship with the mysterious girl next door, he must keep balancing family, work, and the responsibilities resting on his shoulders while continuing to pursue the manga career he refuses to abandon.