Callisto Regulus is a character name from manhwa called "Death Is The Only Ending For The Villainess" or "Villainess Are Destined To Die". He is the male lead of the novel (also the manhwa maybe). He is the crown prince of Ioka empire.
"His name is Callisto Regulus." -System
by I love Diavolo Obey Me November 18, 2021