Rio is the student council president of Millennium. Cold and calculating, she cares more about objective facts than emotions. She is at odds with Himari due to their contrasting personalities. Her nickname is "Big Sister."

Huyan ZhuoWP (呼延灼WP, Koen Shaku?), also known as Assassin of Liangshan Marsh (梁山泊のアサシン, Ryōzanpaku no Asashin?), is an Assassin-class Servant summoned by Ritsuka Fujimaru in the Grand Orders of Fate/Grand Order.