Milly Thompson is a tall young woman with long brown hair and blue eyes, employed by the Bernardelli Insurance Society. She is introduced as the junior partner and assistant to Meryl Stryfe, and the two are assigned to track down and assess the damages caused by the infamous outlaw Vash the Stampede. Milly comes from a very large family, being the youngest of eleven siblings, and maintains close contact with them through regular letters she compiles into a newsletter she calls the Milly Monthly. Her family is deeply important to her, and any disrespect toward them or toward the value of food—especially pudding—can provoke a fierce reaction.

Milly’s outward demeanor is cheerful, friendly, and somewhat absentminded. She often appears ditzy or simple, and her easygoing nature can lead others to underestimate her. Beneath that surface, however, she possesses a sharp intuition and a perceptive understanding of people. She is frequently the first to notice subtle truths about situations or individuals, such as correctly identifying Vash as the legendary stampede before Meryl is fully convinced, though she remains modest about her own insights. Her intelligence also shows in unexpected ways, such as her skill at chess. Despite her gentle temperament, Milly is physically very strong and capable of impressive feats of strength. She carries a large, multi-barreled concussion gun, often called a stun gun, which she conceals under her coat. This weapon fires projectiles that expand into X-shaped claws upon impact, and its blunt force is powerful enough to knock over trucks. Milly wields it with accuracy and control, using nonlethal force in combat.

Her motivations are driven by loyalty, kindness, and a genuine desire to help others. She approaches every situation with optimism and an open heart, quickly accepting Vash as a friend and trusting his pacifist philosophy. Her role in the story is that of a supportive companion who provides emotional balance and comic relief, but she also proves herself a capable ally in dangerous encounters. She and Meryl act as the audience’s viewpoint into the world of Trigun, with Milly’s warmth often diffusing tension and strengthening the group’s bonds.

In terms of key relationships, Milly holds Meryl in high regard, referring to her as senpai or ma’am out of respect, and their partnership deepens into a close friendship over time. She forms an immediate bond with Vash, accepting him without skepticism and offering him unconditional support. She also develops a meaningful connection with Nicholas D. Wolfwood. In the anime, this relationship grows more intimate; the two share a night together before Wolfwood’s final confrontation, and Milly is deeply affected by his death. In the manga, the romantic dimension is less explicit but still implied through her reaction to his loss.

Throughout the series, Milly experiences subtle but significant character development. She transitions from a seemingly naive trainee into a perceptive and courageous participant in the group’s struggles. Her unwavering optimism and compassion remain constant, but she becomes more attuned to the harsh realities around her without losing her core belief in the goodness of people. Her notable abilities include her physical strength, her marksmanship with the stun gun, her emotional intelligence, and her capacity to see the best in others, which makes her a grounding presence in the chaotic world of Trigun.