Milly Harollson is the middle sister of the Harollson family, between Mae and Mika, and the older sister of Max. Although often being childish and ditzy she is a professional monster hunter and is extremely strong.
Milly has long blonde hair with curls reaching past her shoulders and green eyes. She wears a white and blue summer dress, a belt that has pink and white pouches tied to it, black shoes, and tall white socks. Her bust size is the biggest of all three sisters. Her weapon of choice is a large double-sided battle-axe that she can wield with one hand, though she has been seen to use her bare fists to great effect against her foes.
When at home Milly is a very cheerful and friendly girl, always greeting customers with a big smile and a hop of her feet (with other things also doing some bouncing in the process). Despite being older she tends to act like a child most of the time and can come off as stubborn sometimes. She teases Max just like an older sibling would do but cares for him and her sisters greatly which always shows.
When out on a hunt her personality becomes significantly more focused while her cheery attitude vanishes completely. Being the brute force of the trio, Milly often chooses to rush her foes with the biggest and heaviest weapon she can and charge straight into battle. She prefers to use her battle-axe in combat that she wields expertly, though has shown to be able to beat monsters dead with her fists alone. When hunting her carefree nature is replaced with an seasoned warrior's spirit, living up to her reputation as one of the best hunters in Koskaysil alongside her sisters.
Milly is first introduced along with her family in Act VIII when Daniel's group stops at their shop for supplies. After realizing that she and her sisters are professional monster hunters Daniel's group quickly pays for their things and heads back towards their parked carriage so they can leave as soon as possible. Noticing that Triska wasn't given all that she paid for Mika tries to return the missing goods, only to discover Daniel surrounded by monsters and jumps to the conclusion that he's being attacked. With Milly and her sisters quickly arming up they ambush and attack Daniel's mates, injuring Kroanette, Pip, and Alyssa and nearly killing the others before Daniel stops them. Daniel's group attempts to explain that not all monsters are evil but the Harollson sisters don't believe them, even after Alyssa and Specca help them avoid serious injury from attacking Star shortly afterward. Believing that Daniel is at least a good person at heart the Harollson sisters agree to let them all go but warn them never to return again.
Milly is later seen with her sisters when they are given a monster hunting job by order of Queen Leanna. The trio venture off towards the farming village of Rees where they are told monsters have been attacking the locals, however their journey is cut short when they reach the city of Nibelvale, which had been completely overrun and destroyed by a horde of monsters who claim to be part of The Sisterhood. While they are able to slay a good number of the wicked fiends more show up and surround them. It is then that Alice the witch uses her magic to immobilize Milly before repeatedly slamming her into the ground. Although very strong, Milly ultimately dies from the forceful impacts, her death shortly following that of her sister Mae's. Milly is last seen with Mae as they appear before Mika as hallucinations after the battle of Nibelvale, with them assuring her that their deaths weren't her fault and to keep fighting to both protect Max and put an end to The Sisterhood.