The way in episode three (?) Ryu walks into the Golden Gate and asks for a hot milk, it always seemed to me like it was...kind of a way to piss Gai off. Yeah, Ryu's a square, but this is after Ryu's been hounding Gai, and Gai's reaction is like ours -- "Oh, brother. Let's show this nerd!" And he fires off two billiard balls towards Ryu and -- what's this? Ryu spins around and catches 'em. There's more to this Ryu guy than meets the eye...
Now, I like the Ryu character as written, but I wouldn't rank him amongst the best Reds because I think Koutarou Tanaka is too bland and weak of an actor to really pull this character off. Yeah, Ryu is supposed to be a square, but there's supposed to be a lot going on with the character internally -- that this guy is hurting and masking it with a sense of professionalism. This is a Red who has to deal with the most unprofessional and half-together team in the franchise. Tanaka's only capable of playing the Dudley Do Right part of it, and he has no presence, and he makes it so much easier for Toshihide Wakamatsu to steal the show. When, if you look at it...Ryu's a bigger bad-ass than Gai. He's always calling Gai on his ****, he's always one-upping him. He's technically the better fighter because he's a professional soldier. But you have the flashily written Gai, shoving in your face the superficial things that's shorthand for "cool," and he's played by a talented, charismatic actor. After casting Gai, they needed to look at Tanaka and realize they made a mistake. They needed someone who could match Wakamatsu.