On a rainy day, high school student Amane Fujimiya notices his neighbor, the famously beautiful and academically gifted Mahiru Shiina, sitting alone in a park, getting drenched. He offers her his umbrella and runs home, catching a cold as a result. The next day, Mahiru appears at his door to return the favor, but upon seeing the sorry state of his apartment and his inability to care for himself, she decides to step in. The spin-off manga The Angel Next Door Spoils Me Rotten: after the rain adapts scenes from the original light novel's fifth and a half volume as well as a special short story, offering glimpses into the past and present of this relationship beyond the main storyline. It is a collection of sweet and tender moments depicting the daily life of the blunt but kind-hearted Amane and his beautiful, sharp-tongued neighbor as they grow from strangers to something much closer.

The story centers on the evolving relationship between Amane and Mahiru. Initially, their interactions are purely transactional, with Mahiru cooking and cleaning for Amane out of a sense of obligation and a desire to correct his "unsightly" lifestyle. Despite their insistence that they have no romantic interest in each other, the time they spend together in Amane’s apartment slowly begins to blur the lines between obligation and genuine affection. While they try to keep the fact that they are neighbors and close friends a secret from their classmates to avoid unwanted attention and rumors, their bond deepens with each shared meal and quiet evening. The manga focuses on these small, impatient moments in their journey, highlighting the gradual shift from gratitude and convenience to a heartfelt, unspoken connection.