School Days follows Makoto Itou at the start of his second semester of freshman year, when he notices Kotonoha Katsura on the train they both take every day and becomes captivated by her quiet beauty. Too nervous to speak to her, he secretly takes a photo of Kotonoha and uses it as the wallpaper on his cell phone, clinging to a charm that is said to help hidden love come true.
When classmate Sekai Saionji spots the picture, she does not expose him. Instead, she offers to help him win Kotonoha's heart and even befriends Kotonoha herself on Makoto's behalf. What begins as an awkward arrangement quickly turns into an intimate and unstable triangle.
From there, School Days traces Makoto, Kotonoha, and Sekai through the ordinary routines and private insecurities of high school life. Their relationships shift under the pressure of romance, jealousy, loneliness, and misunderstanding, turning small gestures into emotional fault lines. The series builds its mood through everyday moments, then lets those feelings accumulate into an increasingly uneasy portrait of adolescence, where affection and cruelty sit far closer together than any of them expect.