Ryuo Sukuna (龍王 宿儺, Sukuna Ryūō) is the Dragon Lord of the seven seas and the husband of the turtle queen.
Ryuo physically appears to be a man between 20-30 years old with shoulder-length lavender hair that is kept in a short braid and held together using a cylinder shaped hair ornament. He has pale blue skin and fin-like ears as well as dragon horns on the sides of his head. Ryou usually wears an eye patch to cover his right eye, which had long scar on it that was caused by Tomoe, who stole his eye many years ago and his left eye is ocean blue.
Ryou is a proud person who likes a good fight and he knows how to be a good reliable man although his liking of violence is something Kamehime (Ryuo's wife) disagrees with. He always keeps in check what people owe him and can keep a grudge for very long periods of time.
Ryuo came after Tomoe whom had just saved Ami Nekota from drowning in the sea. The Dragon Lord's eyes are known as the Longevity Elixir and are said to give great power to whoever has drank them. Though aggressive and temperamental, he is afraid of Kamehime's (Ryuo's wife) anger. She disapproves of his fights, saying they mar his beautiful face. He is forced to give up his grudge against Tomoe after she befriends Nanami Momozono.
When Nishiki Ryouri attacked Kotarou Urashima and Numano Himemiko in her human form, mistaking her for a regular human, the Dragon King came to Himemiko's defense. After Kotarou was brought to the hospital, he stayed with him, even after Himemiko had gone out to find Kotarou's rubix cube. He told him that Himemiko was a yokai, the Princess of the Swamp. Unable to believe that Himemiko had hid this from him all this time, he tells Himemiko to go away when she comes back with the cube.
After he was released from the hospital, he sits outside with Ryuo. Ryuo asks him if this was the way he wanted to end their relationship, with the harsh words he'd said and that if he wanted to say anything he should say it now and he would pass it on to Himemiko. When Kotarou doesn't reply, he tells him he is troublesome. If he wanted Himemiko to have told him, he should be a reliable man, like himself. Kotarou immediately knows he's right but he'd already disappeared. He looks for Himemiko's swamp and Ryuo appears and helps him finally apologize to Himemiko.
Kamehime is Ryuo's wife whom he loves very much, but he is afraid of her at the same time as she often tells him to stop his senseless fights but he often forgets and ends up suffering her wrath.
Ryuo held a grudge for Tomoe for 526 years ever since Tomoe ripped out his right eye (then stole it) and attacking/ransacking the north gate of Ryūgū Castle. However, after his encounter with Nanami Momozono, a little blackmailing from Mizuki and fear of Kamehime (Ryuo's wife), Ryuo finally let go of his grudge on Tomoe.
- (To Kotarou Urashima) " If you want to be trusted...become a man who's worthy of trust."
- (To Nanami Momozono) "He probably doesn't want to see you. He failed to die because his human kami saved him. and you saw what he was like when he was young and immature. He's probably too embarrassed to see you."
- Ryuo is left-handed, as seen in episode 8 when he writes Nanami a check.