First Manga Appearance: Chapter 25
Name Meaning: Ito=thread; string, Yui=only; unique
Nicknames: Radio taxi (rumoured)
Gangs: Oni-baku Gumi
Current School:Tsujido High School
Previous School: Kamakura P. S. 5
Notable Features: Has a crush on Eikichi; makes odd sandwich combinations; first girl to be part of the Oni-baku Gumi
First appears during the Kamakura Mad Dogs' return to Tsujido & offers to point out Saejima & Kamata's location only if Eikichi takes her out for ice-cream. She reveals the pair's history & warns Eikichi to be careful. She & Tsukai try to stop Eikichi from taking the Kamakura Mad Dogs alone. Her fighting ability is unknown, however, she, along with Tsukai & Abe, arrive to backup Ryuji during his fight with Kamata.
She is seen to enjoy cooking & brings sandwiches to share with her classmates, who finds them repulsive, except Tsukai, revealed to have a crush on Itou & keeps a photo of her in his wallet. The Oni-baku come across the photo & decides to help set Itou up with Tsukai by organising a get together. They ask Itou to bring along her female friends to help themselves in the process.
She goes shopping with Tsukai to get an outfit for the get together. Tsukai tells her about the Oni-baku legend & she sees his admiration for them. They go drinking & she reveals having a crush on Eikichi, wanting to admire Eikichi as much as Tsukai. She notes Tsukai's kindness as he tells her that he will support her.
It turns out that she only invited her ugly friends to the get together so she can attract Eikichi's attention. Her plan backfires when a pretty blonde girl, Kaoru, tags along & all the guys are too busy chasing after Kaoru to notice. She even goes as far as taking off her top but no one notices her, except Tsukai.
She later finds out that Tsukai challenged Eikichi to a fight & thanks to Ryuji, she is able to realise Tsukai's true feelings. She rushes towards the fight scene & tends to Tsukai's wounds. She reveals to Tsukai that she now sees a guy's inner qualities & tells Tsukai that he looks cool. She embraces him & thanks him for everything. They begin dating soon afterwards. It appears that she is always late to their dates.
She was the first to catch wind of Ayumi's resignation & rushes to inform Ryuji of her departure. She rushes to the station with Ryuji, along with Mariko but they were too late. She & Tsukai “kidnap” Ryuji & bring him to his surprise 16th birthday party to cheer him up. She later appears at numerous Oni-baku Gumi gatherings, such as the beach party celebrating the Oni-baku's defeat of Midnight Angel. She also helps Ryuji & Nagisa paint their bus.
It is rumoured that during her time at Kamakura P.S.5, she was known as the Yamiko-Tei gang's radio taxi because all they had to do was call her for sex. However, her boyfriend Tsukai realizes that he loves her & doesn't care about her past. Due to her long time relationship with Tsukai, she has somewhat more experience than the other girls & offers them advice, such as Shinomi’s quest to find the pink elephant.