The first trans characters who appear in Helluva Boss are two humans in the crowd that gathers to watch Verosika's concert in "Spring Broken." One is named Randy, and Milky seduces him. The other gets grinded on during the performance of "Vacay to Bonetown."

Later, the show began introducing trans imps. Of course, by far the most notable of these is Millie's sister, Sallie May, voiced by trans actress Morgana Ignis. Sallie May's horns combine the AMAB color scheme (equally sized black-and-white horns) with the AFAB size and shape (small and thin), and her black hair had a white splotch.

Although Sallie May had little dialogue, she quickly became a fan favorite, with significant amounts of merchandise of her appearing in the show's official store on Shark Robot.

Another background character, this time a fish demon, appears in "Ozzie's." Named Turkoyz, they constitute Helluva Boss's thus far only confirmed nonbinary character.

Lastly, two trans imps showed up in "Queen Bee": a man who recognizes Blitzo while he's in the driver's seat of the IMP van and a woman who sits besides the same man as Blitzo makes out with Dennis.