"Three years and eight months ago. I was given birth into this world. I was bestowed an AI based on the SAINT's data and a mechanical body that could withstand any environment. I, being created as a combat android by the mother of all SAINTs, Matthew, was supposed to be the ultimate android in battle situations. However, I was forced to realize what a foolish misunderstanding that was in my first combat. It was an encounter with Vesper's combat android, V1046-R Mahoro. Combat duration was only four minutes and thirty-one seconds. It was an utter defeat. In one more strike, you (meaning Mahoro) could have destroyed me. But you left without finishing me off. To understand what your action meant, I have trained myself to this day. And to surpass you as a warrior has become my reason for living." (episode 07)

Ryuuga first appears on the seventh episode. He saves Chizuko Ooe from getting run over by a car driven by two escaped convicts (the same men who hijacked the bus in the first episode). Suguru instantly becomes suspicious of him because of the way he saved Chizu -- he's able to jump way up high and hang onto a pole while carrying her -- and he flees from the scene of the crime just like Mahoro did. He claims he doesn't want the police questioning him, though.

He poses as a substitute science teacher in Suguru's class. Why? Because he made a deal with Matthew. In order for Ryuuga to duel Mahoro, he has to do a little bit of investigating first. He's supposed to find out what it is that's so important about Suguru. Is Vesper interested in recruiting Suguru? Does this mere human have some kind of powers? Why is Mahoro guarding him? Is it because she's trying to make amends for killing the father? These are some of the questions he asks himself as he follows Suguru and interviews the latter's friends. When he interviews Saori, she immediately assumes that Ryuuga is interested in Suguru in that way thereby causing him to flush. After all, Ryuuga is popular and gorgeous; he even has throngs of adoring female fans at school. (Saori even imagines both he and Suguru buck naked and embracing... and that Suguru is no longer interested in big breasts.) But although he doesn't care much about his fans, he's not gay.

Anyway, Ryuuga badly wants to defeat Mahoro, Vesper's champion. Ever since he lost, he's trained so hard (in the SAINT's ship, there's a simulation room). He doesn't realize that since Mahoro is six years older than him, she's got more actual (as opposed to simulated) battle experiences. When Mahoro apparently drops her android duties, he thinks that there's a hidden motive. He's formulated a lot of theories, but one thing he doesn't consider is that Mahoro may shut down any time. Anyway, when he and Mahoro fight again in an abandoned building and it seems that he is the one winning, he gets a little bit cocky. After a while, he gets suspicious; he may have trained hard, but Mahoro hasn't exactly lost her deadly skills just because she's gone domestic, er, settled down. Though he's suspicious, he doesn't realize that Mahoro is luring him outside until it's too late. He gets hit by a pure anti-matter beam that she's collected while they were having hand-to-hand combat. Unfortunately, he has a shield/barrier thingamajig that enabled him to withstand the awesome power.

Oh yeah, his weapon/final attack is Break Blade.