Responses
Yan Mingxiu is from "Professional Body Double", written by the same author but it is not A.B.O
As for the Alpha who wears mouth guard, you're probably referring to Song Bailao from Chen Shang (=・ω・=)
Thank you
In chapter 19, the alpha character Yan Mingxiu looks familiar from another bl i read but can't remember. Idk if it's the same but the alpha wears mouth guard to prevent biting on others