The entire narrative of "Horimiya" is a journey toward mutual acceptance and future commitment. After Hori and Miyamura discover each other's secrets, their bond deepens rapidly. Miyamura confesses his love in Episode 4 while Hori is sick, and she accepts, making them an official couple by Episode 5. A significant turning point is when Miyamura cuts his hair, shedding his gloomy persona at school and revealing his piercings, which signifies his growing confidence and trust in his new circle of friends.
Their relationship progresses to include physical intimacy, a topic handled with a maturity rare for the genre. The story also explores Hori's slight masochistic tendencies, where she enjoys Miyamura being occasionally aggressive, which he finds confusing but ultimately accepts as part of her personality. The supporting cast's relationships are also explored, such as Tooru's unrequited crush on Hori giving way to a strong friendship with Miyamura and a complicated, ambiguous romance with Yuki. The student council members, Sengoku and Remi, provide a foil as an established couple, while Sakura Kono experiences her own heartbreak after being rejected by Tooru.
The series finale culminates in their high school graduation. Miyamura has a final, poignant internal conversation with his lonely, middle-school self, fully accepting his past and embracing his present happiness. He reflects on how meeting Hori changed his world from monochrome to color. In the penultimate episode, after Hori expresses her anxiety about the future and being separated, Miyamura informally proposes marriage, which she accepts. The series ends with them walking hand-in-hand, confident in their future together, having found complete acceptance in each other.