Adachi You is Adachi Hana 's younger brother. He is the leader of the 'Big Four' in Ageha High School who were looking for Hana by the time she starts attending school without her glasses and braids. He is currently living in Shinigawa's house.
You has an eyepatch that covers his left eye with a mole on the lower side. He usually seen wearing a uniform with his coat laid on his shoulders.
You is a sleepy person who is alway seen yawning. But unlike Hana, he is intelligent which Shinagawa gets annoyed with when he decided to live with him. He is a caring sibling, when he always sees Hana, he acts like a child and show some sweetness and care in front of her.
You is behind of the delinquents who are looking after Hana when she started attending school without her glasses and braids on. Shinagawa, Izumi, Chiba, Kagawa and Kitami found this alarming for Hana fighting some students again so they decided to look for information but also fighting some delinquents too. They got information from Sagami but he doesn't know that Hana is Shinagawa's classmate. After they found out that the 'Big Four' of Ageha High School is after Hana, they decided to go to Ageha and face them. They soon find out that the Nerima, Shinagawa's childhood friend is part of 'Big Four'. They made a one on one intense fight, Izumi fighting Yamaguchi, Kagawa fighting Nara, Kitami fighting Ou and Shinagawa against Nerima. After they won their each battles, You arrived and disappointed after seeing his men defeated. Shinagawa and the others underestimated him after seeing him younger and thinner thinking he is just a kid. You then tells them that he is looking for Hana to bring her back to their world, meaing changing her back to be delinquent again. Full of confidence that Hana won't refuse to his favor after some explanations Shinagawa did, they started a fight agaisnt him. Unluckily, he beat everyone with a kick and he told them that he is Hana's younger brother.
They are held captive to use them for Hana agreeing in his request. He then reveals that he needs Hana's assistance to conquer the nation which he is serious at. Shinagawa and the rest are saved by Akita after he is being called by Kairi which Chiba asked for help. You and Akita had a fierce fight and the Shinagawa and the rest made the chance to escape. But then Hana arrived at the scene and give You a punishment by spanking him. You pushing Hana more to come back to their main house, he insults her friends as weaks and he trained himself to become strong as her. But Hana gets mad and tells him she doesn't know him anymore. You runs and Hana acts as if nothing happened between them. Shinagawa asking Hana about her brother not meeting for three years to talk to him, she follows You because she believes that his problems are her problems.
The next day, You pushes himself to live in Hana at Grandma's house but she refuses because she believe there is no more space for him
and if Himeji Rinka leaves, no one will clean the house. He then decided to go to Shinagawa's house through Hana's orders to live there for a day which Shinagawa pisses off. Shinagawa believing You will not have a chance to stay here, he asks Kairi but she doesn't care on whatever Shinagawa do to his room. Thinking You is like his sister who lacks common sesnse, he plays with him like video games, othello and cards, Shinagawa realizes that You is intelligent after he points out the answer in Shinagawa's assignment wrong. He then reveals that despite all of his intelligence, Hana chose Shinagawa over him and he believes after seeing her she changed. Shinagawa gives him some words and tells about Hana before not having friends. He fell asleep and the next day when Shinagawa wakes up, You is not in the bed anymore. When he leaves his room, he saw You cooking their breakfast and You told them that he is staying for a while.