Megumin (めぐみん) is an Arch Wizard of the Crimson Magic Clan in the Fantasy World, and is the first person to join Kazuma's party. She is one of the main characters of the KonoSuba series. Megumin is a straightforward girl, who speaks in an old-style Japanese dialect. She can be very hyper and lively at times and has chuunibyou tendencies like the rest of the Crimson Demon villagers. She is very intelligent, but has very little self-control, especially when it comes to using Explosion magic. She has no problem wasting her spell on empty plains or abandoned castles, as long as she can use Explosion once a day.

After being harassed for days by Megumin's Explosion magic, Beldia was pissed and named her as the crazy-headed girl ("Girl with screws loose"). Much to Megumin's dismay, since the nickname describes her quite well, "crazy-headed girl" also became her official nickname in Axel. Kazuma stated that Megumin has the most common sense among the girls in the party, but considering her competition, it is not much of a compliment. Megumin also enjoys participating in (or starting) childish antics with Aqua or Darkness, and often acts over-dramatic to hype up the moods.

Megumin is generally calm and cheerful, but she can easily become aggressive when she feels slighted or challenged. Kazuma stated that she is magnanimous and cherishes her comrades more than anyone else. This is evident as she will become fiercely protective when others mock or try to hurt her allies. She also hates being treated like a child just because of her young appearance, and becomes despondent when people call her a loli.