Doctor Gia was an anime-only character. He appeared in the Stars season as a surgeon from America who came to Japan to perform a life-saving operation on Misa, in episode 185.
Sailor Aluminum Seiren thought he was a good target for a Star Seed and attacked him, but was disappointed when it turned out to be a blank. He then turned into the Phage Sailor Doctor, and was saved by Sailor Mercury and Eternal Sailor Moon. After he was back to normal, he successfully performed the operation and Misa recovered.