Riko Amanai is a character in the Jujutsu Kaisen series. She was a student at Renchoku Girls' Junior High and the designated Star Plasma Vessel for Master Tengen's merger in 2006. She's 14 years old. Riko is an outspoken and feisty young woman who appeared to steadfastly believe in her role as the Star Plasma Vessel. She tried to keep up an aggressive facade at times, but she's really just a normal teenage girl who's been thrust headlong into the jujutsu world.