One day, Shota-kun's older brother brought his girlfriend home. She was Yuka, a sweet and incredibly cute older sister figure—and she had huge breasts! Shota-kun couldn't take his eyes off her cleavage. When his brother left to meet up with friends, Shota-kun found himself alone with Yuka. They started playing Othello, but Shota-kun's gaze kept drifting back to her ample chest. The story unfolds as their intimate connection deepens.