Raritty
I imagine celestia got tired of seeing her male students distracted with raging hardons, touching themselves while she tries to teach and trying/failing to hide the tent in their pants when they’re called to the front of the class. Fed up, and turned on, she presents herself for any of her students to take turns having their way with her before class starts, so they get it out of their system. Most of them end up draining their pent up balls inside her pussy, not many of them being able to last a minute before unloading hard inside her.