Ryo Urawa possessed one of the Seven Great Youma, Bunbo, which gave him psychic powers. He used these powers to score well on tests. He admired Ami who had natural intelligence and had a crush on her. He is aware of himself being a Youma and Ami of being Sailor Mecury. He foresees himself turning into Bunbo and asks Ami to kill him when it happens.
Even after being transformed back into a Yhouma, Ryo was able to keep control of himself for a short time and attacked Zoisite. But Zoisite gets him under control and sends him after Sailor Mercury. Sailor Moon and the others show up and working together they are able to return him to his human self.
He is transferred to another school and has to move away. He returns to warm Ami again and warns her of Beryl's plan to revive the Seven Great Youma. He is captured again but the Sailor Senshi frees him and the other former Seven Great Youma. Later he is seen hanging out with Ami. Like most anime-only characters in the first season he does not appear in the later seasons.
It is a fairly popular shipping. He was seen as a good match for Ami with similar interests. They got a good amount of ship-tease in his episodes. It rivals other Ami pairings.