Riko is a young slim girl with long dark hair which is braided in the back and extends past her shoulders. She is always seen with her light hairband on the top of her head and normally wore her school uniform.
The uniform was designed with striped cuffs and collars on a white long sleeved shirt with a black skirt, black stockings, and black shoes. She has also worn a black dress with white shoes. While at the beach, Riko wore a straw hat, a white hooded jacket, and a black top and bottom swim suit.
Riko is an outspoken and feisty young woman who appeared to steadfastly believe in her role as the Star Plasma Vessel. She tries to keep up an aggressive facade at times, but she's really just a normal teenage girl.
Riko cares deeply for her caretaker Misato Kuroi and enjoys spending time with her friends at school as well. When Kuroi was kidnapped, Riko's escorts offered to handle it themselves but she wanted to help. Riko quickly becomes flustered when it comes to people she cares about and her ability to be with them, usually crying when that is in question.
Without a traditional family, Riko initially embraced her fate as the Star Plasma Vessel because she thought she was alone. However, after spending time with her escorts Satoru and Suguru along with Misato and friends at school, Riko ultimately decided she wanted to live out her life with everyone instead of merging with Master Tengen.
Riko is found to be a match to merge with Tengen, which she doesn't mind. As Riko, along with Misato, are waiting at a location for Suguru Geto and Satoru Gojo, when they are suddenly attacked by soldiers of Q. Riko is rescued from the Q soldiers by the arrival of Geto and Gojo. After the Q soldiers are defeated, Riko wakes up and wonders who Geto and Gojo are. Misato tells Riko who Geto and Gojo are, which the two wonder why Riko is so spunkier. Riko explains to them how she views the merging with Tengen, and starts to yell that them with they stop listening to her. Riko suddenly notices that she is really late for school, and has them take her to school.
Riko then attends her classes when she arrive at her school, but doesn't have Geto and Gojo stay by her side. Riko is attending music class, when Gojo arrive and drags her away since intruders have invaded the school. As Riko is being brought to the college by Gojo, the two encounter an intruder who is capable of cloning themselves. As Gojo takes out the intruder, Riko gets a phone call and informs Gojo that Misato has been captured by the enemy. After receiving information from the kidnappers, Riko discuss with Gojo and Geto about how they will rescue Misato. The three then heads to Okinawa and manage to rescue Misato.
After the rescue, the four decide to enjoy Okinawa before heading back. When its time to leave, Riko convinces the others to stay one more day. The next day, the four leave Okinawa and arrive at the college but are suddenly attacked by Toji Fushiguro. Riko is quickly brought into the college by Misato and Geto, while Gojo faces the enemy. Once the three reach the Tombs of the Star Corridor, Riko and Misato have a tearfully goodbye. Afterwards, Riko and Geto head further into the tomb while leaving Misato behind.
Once the two reach the main chamber of the tomb, Geto give Riko direction on were Tengen is at. When Geto tells her that she can also leave, Riko explains how she was originally okay with the merge but know she just wants to be with everyone some more. Geto then says that he will take her away, but Riko is suddenly shot in the head by Toji. After Geto is defeated by the enemy, Riko's body is taken to the headquarter of the Star Religious Group. Later, Riko's body is taken from the Star Religious Group by Gojo.
Abilities and Powers
Overall Skill Level: Riko is a non-combatant, however she can still see curses and has a good understanding of the workings of jujutsu. She likely learned this after discovering her status as the Star Plasma Vessel, a perfect match for Master Tengen.
- Riko's surname contains the kanji for "sky" (天 ama?) and "within" (内 nai?), and her first name contains "logic, reason" (理 ri?) and "child" (子 ko?).
- Riko is probably a second-year in Junior High.
- Riko doesn't like shiitake mushrooms, but Misato has been secretly mixing it in her food. She's actually eaten a lot.
- Riko is not allowed to go much, so she's happiest when seeing her friends at school.
- According to Jujutsu Kaisen Official Fanbook: