Childhood friends Yuu and Tsubomi attend the same cram school to prepare for college entrance exams, supporting each other to improve their grades. However, feeling anxious over Tsubomi's rapid progress, Yuu devises a plan that throws her into confusion. Realizing the wrongfulness of her actions, Yuu sincerely apologizes to Tsubomi. As they finally open up and speak honestly after a long time, their suppressed feelings begin to surface, eventually leading them to fall in love, passionately embrace their desire, and become one through intimate lesbian encounters including the 69 position.