Romanization help, artist's name is driving me nuts

Anyone's got any idea how to romanize りゅー?

I don't know if you already know about this, but I've been having to use this when getting at artist because I know virtually no katakana.

http://www.smacked.us/acies/pixiv/

"りゅー" = "ryuu" and means "dragon". Also this one's hiragana, not katakana.

Thanks