Yuu's student life, living alone in a dorm after leaving home, is coming to an end as graduation approaches. On the way back from the graduation ceremony, he reunites with his stepmother, Marina, who runs up to him with a smile, rekindling the feelings he had kept hidden. That night, after celebrating graduation together, Marina, having had too much to drink, is escorted to a hotel by Yuu. As he tries to suppress his overwhelming feelings and leave the room, Marina gently kisses him, saying, 'This is my graduation gift to you...' And thus, the boy begins to climb the stairs to adulthood.