Tomoko is a slow-witted girl, earning her the nickname Toroko (Slo-mo-ko in some English translations), she makes up for her slow wit with her huge breasts. She’s also fairly clumsy, messing up things that people normally wouldn’t mess up. Her introduction features her messing up a plan by Miyabi to seduce Onizuka, which gets her expelled from Miyabi’s group.
Tomoko, Miyabi and Urumi are all childhood friends, having attended the same elementary school.
After being isolated from Miyabi’s friend group, Onizuka befriends her… and enters her in an idol contest. Due to her improv talents, she doesn’t win the contest, but finds herself getting picked up by an agency. She, like other girls, develops love for Onizuka as well.
It’s clear from… everything… that Tomoko will eventually be a very famous and successful idol.