Riri Shushu no subete
All About Lily Chou-Chou follows two boys, Shūsuke Hoshino and Yūichi Hasumi, from the start of junior middle school when they first meet, and into second grade. The film has a discontinuous storyline, starting midway through the story, just after the second term of junior high school begins, then flashes back to the first term and summer vacation, and then skips back to the present.
In elementary school, Hoshino was one of the best students in school, but was picked on by his classmates. Hoshino and Hasumi meet and become friends when they join the kendo club, and Hoshino invites Hasumi to stay over at his house. Hoshino's family is wealthy in comparison to Hasumi's family. Hasumi mistakes Hoshino's attractive young mother for his sister.
The kendo club summer camp training is tough, and Hoshino, Hasumi and some other first-grade boys decide to take a trip to Okinawa. Once there, Hoshino has a traumatic near-death experience and his personality changes from good-natured to dangerous and manipulative. Back at school in September for second term, he takes his place as class bully and shows his newfound power by ruining the lives of his classmates. An alternative voice, that of the character Sumika Kanzaki, attributes Hoshino's personality change to the collapse of his family's business and his parent's divorce; this matches several scenes connecting the decline of Hoshino – who has had to change his name – to divorce.
Hasumi, the confused and shy former friend of Hoshino, finds himself sucked into his now-tormentor's gang. He is ridiculed and coerced into doing Hoshino's dirty work, and finds solace only in the ethereal music Lily Chou-Chou makes, and acting as web editor for his fan website. Things become far worse for everyone when Hasumi is assigned to supervising Shiori Tsuda, whom Hoshino has blackmailed into enjo kōsai, and another girl is raped by Hoshino's lackeys after unwittingly offending the school's girl gang. The whole quagmire comes to a head when Hasumi heads to Tokyo to see a Lily Chou-Chou concert, where he encounters the last person he thought would be there.
The story of Hoshino and Hasumi is paralleled by messages posted to a Lily Chou-Chou message board which are displayed on screen. Until the meeting at the concert, it is left up to the viewer to figure out which characters in the story are posting under what names.
violence, cult, murder, sadist, flashback