Hero

In a futuristic world where humans and mermaids coexist, the life of mild-mannered office worker Stephan is upended when he is suddenly proposed to by Chao — a princess from the mermaid kingdom. With no time to make sense of what's happening, Stephan soon finds himself living with the unpredictable, wholehearted Chao, and her sincere love begins to break down his emotional barriers.

Rikka is a ninja descendant. Her grandfather Hyoe is the last chief of their ninja clan and her father is a cyborg researcher. Both are killed when a weapons' company raids his lab to use his research. Rikka sets out to avenge their deaths.