I Don't Like You at All, Big Brother!

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—!!) (referred to as OniSuki for short) is a Japanese seinen manga series written and illustrated by Kouichi Kusano which began serialization on Futabasha's Web Comic High! service from August 2008. 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.

Plot
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 already died. After Nao learns the fact, she wants to normally fall in love 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.