Keine Kamishirasawa from Touhou. Her base character isn't very special, she's just a kind and protective woman who's also a teacher. However, since her hakutaku form makes her grow ox horns, I imagine Keine becomes similar to a cow girl (with milkers) during a full moon, therefore she's also angrier since she's stronger and more animalistic in her hakutaku form (even though only bulls get angry easier)

image is ai generated locally with stable diffusion

The regular message is just a normal introduction.

The alternate message is just NSFW stuff