The 15 year old protagonist. Ryuuji's parents are "Lost Precious" hunters like the rest of his family, as such he lives mostly on his own. He does not know why Rose knows him. It is indicated that they have met each other years ago, when Rose saved Ryuuji from an untimely death. Ryuuji has a vague memory of when he was younger and saw Rose hatch from her egg in front of his eyes. Ryūji is a level 10 breaker, said to be the highest level of breakers who go to find/use lost precious. Besides Ryuuji, there are seven other level 10 breakers (Ryuuji is the youngest of the level 10 breakers).
Later, he is recognized by some of the other dragons as Rose's fiancée, but this is due to a misunderstanding. He truly has feelings for Rose and does care about her, but has yet to be confirmed. This is evident when he first "Engaged" with Rose, which allows him to borrow Rose's power to achieve unbelievable power.