Sei, who lived in the dormitory during his school life, found that his fulfilling three years had come to an end as he finally reached his graduation ceremony. Due to the awkwardness caused by his father remarrying his crush, Mariko, Sei hardly ever went home. However, on his way back, Mariko, now his stepmother, suddenly visited him to celebrate his graduation. That night, at his lodging, she said, 'A present for the grown-up Sei' and gently kissed him―. Guided by his beloved stepmother, he took another step towards adulthood...
