Milly Thompson is a fellow Bernardelli agent and friend to Meryl, serving as her assistant. Although Milly is physically taller than Meryl, she looks up to her, always addressing her as "senpai" or "Ma'am" in the English version, out of respect for her seniority.
Despite being very strong physically, Milly appears somewhat simple and scatterbrained. However, she has an extremely kind heart and shows a strength of character and genuine optimism. When someone disrespects their family—or wastes food, especially pudding—Milly can be just as hot-tempered as Meryl. She might seem a bit dim at times, but she possesses some remarkable skills, such as chess playing, which hint at a deeply buried intelligence. Additionally, she tends to go overboard when drinking.
Milly picked up on the fact that Vash is the notorious Stampede before Meryl did, although she was still somewhat surprised upon realizing she was correct. Coming from a large family, Milly writes letters to them constantly, known as "The Milly Monthly."
Incredibly, Milly manages to conceal a heavy concussion gun (referred to as a "stun-gun") under her coat. The shots from this gun expand into an X-shaped claw and are powerful enough to knock over trucks. At one point, Milly refers to herself as "Stun-gun Milly."
