Ruri is a reliable and good-student honour student, while Yukari loves reading and is laid-back. The two have contrasting personalities, but they have one thing in common - they're both A-cup breasts. When the two start dating and find out this fact, their relationship quickly closes. Then one day, they find out that Yukari's extra classes might overlap with their long-planned summer vacation trip. Wanting to go on the trip somehow, the two gather at Ruri's house and start studying for the retake exams, but...