Sion is the crown prince of Sunkland. In the original timeline, he sided with the revolution army and was among those who pushed for Mia's execution, eventually earning the title "Penal King."
Things play out differently in the current timeline. Mia goes out of her way to avoid him—she's desperate not to end up on his bad side and definitely wants to skip the whole execution thing. Naturally, that doesn't work out. Despite her best efforts, they end up becoming close friends. The relationship goes both ways too; Mia becomes someone Sion looks up to and wants to emulate.
Content compiled by AnimeList.moe from publicly available sources.
