Mangas

余の名はズシオ -  My Name Is Zushio -  My Name Is Zusio
From Anime New Network: Zushio was to be king and promised his sister that he would become king (on penalty of death). Unfortunately for him, his empire was overthrown and now he's a wanted man. A girl has the misfortune of running into Prince Zushio and becomes tangled in his plight. Adding to her misfortune, Zushio is not quite right in the head, but hey, at least he seems to be immortal.
My Bride is a Mermaid -  SetoYome -  The Inland Sea Bride -  瀬戸の花嫁
2002
Un jeune garçon est sauvé de la noyade par une sirène. Mais d'après la loi des sirènes, si un humain voit la vraie forme de l'une d'entre elles, ils doivent tous les deux être tués.Pour lui, l'unique solution au problème est de l'épouser. Mais pourront-ils garder ce secret caché ?
余の名はズシオ, My Name Is Zushio, My Name Is Zusio, My Name​ Is​ Zushio
Zushio was to be king and promised his sister that he would become king (on penalty of death). Unfortunately for him, his empire was overthrown and now he's a wanted man. A girl has the misfortune of running into Prince Zushio and becomes tangled in his plight. Adding to her misfortune, Zushio is not quite right in the head, but hey, at least he seems to be immortal.