Gill

Gill is a female fishman who, like many other people, was drawn into the world of Arbatel by the magic of the Grimoire and is currently a member of the swim club and a student at the Grimoire High School. She makes their debut in Chapter 77.

Zoological Classification
Fishfolk are a pseudohuman race resembling, in affect, humanoid fishes with arms and legs, and with webbing between their fingers. Fishfolk are capable of breathing air and, ironically enough, are more capable on land than the far more humanoid Mermaids thanks to their functional legs.

Trivia

 * Although the description in Chapter 79 states that Gill is a Fishman, she looks very different from Sebasstian and Flounnder. This could be because female Fishman may be more humanoid than males of their species, just like by Minotaurs and Kobolds. Alternatively, it is also possible that Gill belongs to a different Fishfolk subspecies than Sebasstian and Flounnder.
 * Gill is the second monstergirl in the series after Draco to be revealed as a lesbian with the following one being Aya.