Ryo is unlike the generic, blend, featureless leading male you find in most other anime shows. He is definitely one with a character. As a 3 years old child he alone survived an airplane crash in Central America, which probably killed both of his parents. Because of this he himself does not know of his own birthday and nationality, or even his full name. To survive he joined a village which belonged to the rebels in a country in the midst of a civil war. He was trained to be a guerilla from the youth and he became one of the best. After the civil war, which the rebels lost, he and others were kicked out of the country to America. There he started to work as a gun for hire. After a while he came back to Japan. While pretend to be an apartment controller in Shinjuku, Tokyo, he started his career as the "Sweeper" (From the original Japanese translation, or literally means "the one who cleans up the street", or "Street Cleaner". I prefer to call him a "Trouble Shooter".) Ryo likes to work for beautiful women, mostly as bodyguard and/or finding missing people, etc, while taking out a drug ring or gangster or two on the side.
Ryo LOVES Kaori Makimura, but he refrains from express his love for her simply because it will put her (or any other woman) under danger in the line of work he is doing. Instead he covers it up and Kaori becomes the only woman who can not get Ryo excited (on the appearance). Once he said "Woman can fall in love for the rest of her life, I can only fall in love once a while".