I Don't Like You At All, Big Brother!! Vol 3–4

Takanashi Nao's massive crush on her adoptive older brother Shuusuke grows, but her best friend Iroha will not be overshadowed. She desperately competes for Shuusuke's affection in an ever-escalating battle. Meanwhile, class president Mayuka has introduced a secret weapon that Shuusuke can't possibly resist. As Nao and Iroha strive to outdo Mayuka, frisky Shuusuke struggles to keep his cool - and more importantly, his sanity. Collects volumes 3-4 in omnibus format.

Source: Anime News Network Encyclopedia