" You are going to pretend to be me, and sing on stage for the first half of the concert !!! "
Except that Momoka has brown hair and much smaller breasts, there is no real physical difference between them. This allows the girls to even pose as each other, which Momoka realizes, and confronts Urabe personally in hopes that she will agree to her plan of switching between model and student. Urabe, however, completely turns her down, not being interested in a life of an idol. But after a little quarrel which ends with Momoka's clothes being shredded by Urabe's scissors, Urabe takes her to her home where the girls further become acquainted with each other.
After seeing Urabe and Akira's bond, she goes with her promise and lets go of her plan to switch places, however not before stealing Urabe's uniform and going on to make Tsubaki taste her drool. It is revealed she wanted to become a "normal" girl due to an incident with a boy she had a crush on before she became famous. Then after being discovered and becoming famous, she finally worked up the courage to confess her feelings to him, but before they kissed, he asked if he could tell his friends he was dating a famous girl. Realizing he only liked her because she was famous, she high kicked him in the head.
She appears again during Mysterious Movie Production arc, posing as Urabe and helping promote her school movie.
Appearance and Similarity with UrabeSimilarity between Momoka and Urabe is so significant that they are essentially "twins". In terms of their appearance, there is no real difference between them, except their hair color and breast sizes. If one or the other puts on a wig, or dyes her hair to match, and then hides her breasts under clothes, many people are unable see difference between them. Even those as close as Tsubaki, or Momoka's manager, cannot tell the difference.
Their similarity, however, goes even beyond physical appearance. Similar to how Urabe uses scissors in defense, Momoka high kicks, and is forced to wear restraints. Both devices the girls then hide near their panties.
Another thing is that both girls have similar abilities to perform as idols. Although Momoka is little better here due her experiences, still, Urabe is good enough to hold the audiences attention during the first half of a big concert on her own.
But in terms of their personalities, the girls have few similarities, too, that being mostly while Urabe is more calm and reserved, Momoka is more energetic and lively.