Tsuzuku Ryūdō, second among four brothers at 19 years old, exhibits a polite and insightful nature. His appearance draws frequent female attention, yet he remains humble about it. Preferring irony and sarcasm to physical confrontation, he nonetheless displays considerable combat skills and strategic planning when conflict becomes unavoidable. He shares strong bonds with his brothers: offering advice and mentorship to the eldest, Hajime; engaging in playful banter with the third brother, Owaru; and showing protectiveness toward the youngest, Amaru.

He is one of four reincarnated Dragon Kings from Chinese mythology, the Red Dragon King of the Southern Seas. In dragon form, he commands fire, electromagnetic energy, and nuclear energy. While the brothers favor ordinary lives, they are forced into conflict when targeted by external forces seeking global dominance through technological and economic manipulation, including the "Four Sisters" organization and their associates, the "Bulls."

His relationships extend to the brothers' cousin, Matsuri Toba, whose company he enjoys. He dislikes their uncle, Seichirō Toba, due to his greed and manipulative behavior. Across official media like the original novels and OVA adaptation, his role highlights his tactical mind during the brothers' missions against their enemies. His dialogue showcases his wit, such as a dry remark about swimming with a car during a helicopter pursuit after Owaru's suggestion.