"It hurts, I don't want to have sex." Nei, a second-year university student, broke up with her boyfriend due to their incompatibility . It all started when she complained about it to Yamato, a classmate who happened to be there. "Well, why don't you try to satisfy me, too?" he asked, as if asking to go out for dinner. Nei casually accepted Yamato's invitation, and they became sex friends. Simply put, with Nei's words, their sex was instant. It was as simple as pushing her underwear aside and inserting. Yamato was popular, a playboy, and a little hard to pin down. Their physical compatibility was perfect. They would contact each other whenever they felt like it, and they would have instant sex in the empty classroom 303. It was a relationship based solely on sexual desire, with no love or romance, but Nei thought that was fine. However, this relationship continued for two years, and Nei gradually became addicted to Yamato. There was no love between them, it was pointless to get excited, and they shouldn't get serious. (It seems I was the only one who was addicted to this relationship...) Telling herself this, Nei tries to "graduate" from Yamato, but... "I didn't mind if there were any hard feelings afterward, right?" "I don't want a casual, easy relationship, I want a complicated, serious one." Just as Nei is troubled by the painful, unsatisfying sex she has with her ex-boyfriend, a popular, flirty classmate approaches her and they become friends with benefits.