Mignon Beart was designed to be a contrasting rival to Athena Asamiya. Keywords to creating her persona were "innocent, honest, and a little childish", which Falcoon admits is best seen through her actions rather than her figure. Her design is based on typically "cute idol" traits, particularly her boots, her manner of referring to herself in third-person, and her alternate catgirl costume. Her magical powers were created to counter Athena's Psycho Powers, which is interpreted by Falcoon to be akin to witchcraft.

She was initially not well received by Ureshino and other veteran staff, deeming her to not entirely fit the mood of the King of Fighters universe -though they lightened their impressions after considering the presence of Psycho Soldier members and other "orthodox" characters. As her character further developed, she became the "stupid, but cute" character, Ureshino using the term as a simple means of endearment.