I Don't Like You at All, Big Brother!! (Japanese: お兄ちゃんのことなんかぜんぜん好きじゃないんだからねっ!!, Hepburn: Oniichan no Koto Nanka Zenzen Suki Janain Dakara ne!!; literally: "It's because I Don't Like Big Brother at all, isn't it!!") (referred to as "OniSuki" for short) is a Japanese seinen manga series written and illustrated by Kouichi Kusano which was serialized on Futabasha's Web Comic High! service from August 2008 to September 2016. It has been licensed in North America by Seven Seas Entertainment. It has been adapted by Zexcs into an anime series which aired in Japan between January 9, 2011, and March 27, 2011. An additional original video animation (OVA) episode has also been released. A character song CD and a mini-CD soundtrack was adapted from the anime.

Nao Takanashi loves her brother Shūsuke despite the incest taboo. Nao thinks that Shūsuke is her blood relative, but in fact she is an adopted daughter, whose parents have died. After Nao learns the fact, she wants to fall in love normally with Shūsuke because siblings by adoption can marry under the family law in Japan. However, she finds herself competing with Shūsuke's childhood friend, Iroha Tsuchiura, and his class president and yaoi lover, Mayuka Kondō.