Majima Rei is a practitioner of a martial art born from the battles in the Sengoku era, the Jinnai style jujutsu. During middle school he was a delinquent but, when he became a highschool student, he swears that in order to surpass the one said to be the strongest practitioner of the Jinnai style in history, the 8th head Jounouchi Masashi, he will become the strongest martial artist in the world. For that purpose, he battles against various types of martial arts and fighters.