The Koinobori yakuza gang takes pride in possessing exceptionally valuable souls for the demon world's soul bank. But the arrival of their heir, Ryuji, with his pure soul brimming with fairies and angels poses a challenge to their legacy. As a solution, Maria is assigned the role of Ryuji's personal cupid and is expected to transform him into a suitable member of the debaucherous Koinobori family.