Hajime Ryūdou, 23, is the eldest of four brothers. After the deaths of their parents and grandfather, he became the primary guardian for his younger siblings. He once taught History at Kyowa College, founded by his grandfather, but his uncle, Seichiro Toba, orchestrated his removal. Despite this, Hajime steadfastly upheld his family responsibilities.

He maintains a generally calm and composed demeanor, yet displays fierce protectiveness when his family is threatened. Possessing exceptional physical strength and combat skills, he is the most formidable fighter among the brothers. His relationships with his siblings vary: he shares mutual respect and intellectual companionship with the second brother, Tsuzuku; acts as a mentor to the third brother, Owaru; and exhibits deep protectiveness towards the youngest, Amaru. Their cousin, Matsuri Toba, lives with them, managing household duties. A subtle romantic tension exists between Hajime and Matsuri, though both consciously maintain boundaries.

Hajime is secretly the reincarnation of the Blue Dragon King of the East, one of four divine Dragon Kings. In dragon form, he commands the fundamental force of gravity. This power, like his brothers' abilities, manifests under extreme duress. While the brothers prefer ordinary lives, external forces seeking to exploit or destroy them force them into conflict. As their leader, Hajime strives to protect his family and oppose the "Four Sisters," an organization backed by powerful American interests linked to the "Bulls" – the ancient adversaries of the Dragon Kings. Historically, the Bulls gained dominion over the Western world, while the Dragons retained authority over the East. Hajime fights to prevent the Four Sisters and Bulls from achieving global domination through technological and economic manipulation.