Original title: Lowすぺっく!?～オレと年下妹（カノジョ）とせいきょーいく！～
Reiji is the acting manager of the Shidou cram school and also acts as the guardian for its students. As their ‘onii-chan’, he looks after his imouto Riina, his best friend’s imouto Miko and close sisters Hane and Sora. However, they grow cuter and more ladylike day by day, unintentionally arousing him to his limit. Will he be able to keep his hands off them or will their innocent temptations be too much to resist?