“Let’s have a battle, Onii-chan!”

Shirayuki Hayato is a working adult who lives together with his younger sister, Yuri. While he works, he spends his days taking care of his younger sister in place of their parents who aren’t around.

In public, Yuri is the perfect girl. Kind to everyone around her, she is well-respected and an honors student but when it comes to chores, she leaves that to her big brother. Seeing how she lazes about while being laser-focused on video games, Hayato wishes that she could be a bit more like a normal girl. In the end, he just ends up spoiling her anyway.

Yuri’s good friend, Arisugawa Ruru often visits the Shirayuki household and he often spends his days with the two of them.

Should he watch over Ruru and Yuri as an older brother, or act towards them as a man? As he accepts Yuri’s challenge, Hayato’s trouble-filled days continue…