オーディン

Odin is the main antagonist of Fortissimo//Akkord:Bsusvier. His role is extended in Fortissimo EXA//Akkord:Bsusvier. He was the one who recreated the battle royale, known as Ragnarök. Because of his powers, Sousei looks a lot younger than he is.

fortissimo Wikia

His real name is Yoshino Sousei (芳乃 創世). He is the blood father of Reiji and Ryuichi's adoptive father. Because of his young appearance, he can be mistaken as Reiji's brother (if he had one)./