Both. The one with short red horns & the one on the devlog. The one with short red horns on the main page of the game. Last photo.
Viewing post in World's Crossing Academy Season 1: Janitor Arc comments
The one with the short red horns is an upcoming character with a rather complicated story. She's been in the planning phase since before the game was launched, and I'll probably introduce her during the Security Arc, which is next after the Janitor Arc concludes.
The other one is a Shadow Dragon, and was created by one of our T5 Patreon supporters :)