Bird has an apartment at the very top of a skyscraper, right across from the Talon headquarters in Japan. It makes a very good observation post; he has an old grudge against Talon.
Old indeed; he turns out to be Dr. Mericus' prototype cyborg, RX-606, who had run away earlier and faked his own death in his getaway. He isn't as refined in his techniques as Sonnet, but he has more brute force to toss around. Bird had left because he agreed neither with Talon's plan for the world nor their estimate of him. By the time of the show, he has come to terms with himself, and considers himself as human as any of the characters (and a great deal more than some). He's pretty much an all-around nice guy, with a few prostheses that help greatly in the fine art of kicking the crap out of the forces of evil.
There are hints, towards the end of the series, of a possible romantic entanglement with either Sonnet or Lan. Personally, I think Bird is in the process of falling in love with Lan; when he thought he was about to die, for instance, he said her name. The communion between him and Sonnet, on the other hand, I believe is due in large part to the fact that each is the only one who really understands what it is to be an esper-cyborg.
Bird is voiced by Hironaka Masashi.