Riko Amanai (天あま内ない理り子こ Amanai Riko) is a student at Renchoku Girls' Junior High and the designated Star Plasma Vessel for Master Tengen's merger in 2006. Riko is an outspoken and feisty young woman who appears to steadfastly believe in her role as the Star Plasma Vessel. She tried to keep up an aggressive facade at times, but she's just a normal teenage girl who's been thrust headlong into the jujutsu world. Riko is a social girl who cares about her personal relationships.