Merrill is a main character from the anime Rune Soldier. She is a young thief and a member of the Orphan Thieves' Guild in the city of Phan, where she works under the codename system known as the Cats, which designates pickpockets. She is sixteen years old, with short brown hair and green eyes. She often maintains a dual identity, engaging in theft alongside various part-time employment opportunities, and is frequently preoccupied with earning money.

In terms of personality, Merrill is pragmatic and no-nonsense, approaching situations with sharp wit and intelligence. She is fiercely independent and values the freedom and flexibility that her life as an adventurer provides. Despite her tough exterior and often cynical outlook, she has a softer side and cares deeply for her friends, showing fierce loyalty and a willingness to put herself in danger to help them. She possesses a strong sense of justice and does not hesitate to act against those who would harm others.

Merrill's primary motivation is financial gain, but her loyalty to her companions and her desire for adventure also drive her. She is initially skeptical of Louie, the unconventional mage who joins their party, but over time she learns to trust him and works alongside him despite his unpredictable behavior. Her role in the story is that of the group's thief and scout, using her stealth and thieving skills to navigate traps, gather information, and acquire resources. She often voices caution and skepticism, balancing the more impulsive personalities of her teammates.

Merrill's key relationships include her fellow adventurers Melissa, a priestess, and Genie, a fighter. The three women originally form a party before meeting Louie, and they share a close bond. Merrill's dynamic with Louie is marked by initial mistrust and frequent exasperation, but they gradually develop mutual respect. She also has ties to the thieves' guild and other underworld figures in Phan.

Over the course of the series, Merrill undergoes subtle development, showing increased willingness to rely on her teammates and to act selflessly. She maintains her independent streak but grows more comfortable within the group.

Notable abilities include expert thievery, pickpocketing, lockpicking, climbing, and stealth. She is also resourceful and quick-witted, often using her environment and street smarts to gain an advantage. While not a frontline fighter, she is capable of defending herself in a pinch, often using a staff or daggers, and her agility makes her a valuable asset in exploration and infiltration.