Senagaki Isaku will be a first-year high school student starting in spring. Her grandfather is the third head of the Senagaki group, a yakuza organization, so she is feared by those around her. However, starting from spring, she hopes to make normal friends and normally fall in love. She is admitted into a high school further from her hometown, however, the overprotective young head of the Senagaki group, Utou Keiya, (26 years old) falsifies his age and enters the school with her through a backdoor admission…?! Keiya proclaims that love is too early for her although Isaku is perfectly ready. In truth, she has held an unrequited love for Keiya for quite some time.

Kyoko, a young Japanese girl training to become a professional mermaid, is saved by her coach's mouth-to-mouth "kiss of life". Desire awakens within her, she finds her mermaid voice and discovers the devastating effects of her singing, which will lead her to face the other side of the world.