Ririka Momobami was the Vice President of the student council in the Hyakkou Private academy in Kakegurui. She Was the twin sister of Kirari Momobami whose family was aligned with the family of Yumeko Jabami.
Throughout the series, her identity was mostly hidden by a white mask and with the use of voice distortion. She was considered a stoic and observant person with a cold side.
Though quiet, she seemed to be in step with her sister Kirari. Her cold demeanour was seen wavering when she was utterly shocked when Midari Ikishima took out her own eye to pay back a debt.
It was later revealed that without her mask Ririka was quite the opposite of what she appeared to be.
She was shy with a socially awkward personality with a visible lack of self-confidence. Even though a complete opposite of her twin, she was able to brilliantly disguise herself as Kirari during the meet with their family.
For Ririka, acting as her sister was also a type of mask for her. Shielding her from the terrible outside.
Ririka was shy but that didn’t mean she was without skills. She was able to catch Rina Obama’s trick at one look and was a gambling master which could be the reason why Kirari had so much power within the clan.
Despite her socially awkward personality, she was extremely manipulative when she forced Mary Saotome to gamble against Miyo Inbami and Miri Yobami at the same time staking Yumeko Jabami’s life.
Though eventually, Ririka came out of her shell through friendly interactions with others like Mary Saotome. As she gained more confidence in herself, she started removing her mask more often.
But this came with a disadvantage. The more Rirari developed into her own person, her ability to blend in with her sister diminished.
In the first season, Rirari wasn’t seen doing anything. She was just present at all student council meetings, listening silently without saying a single word.
After Mary ripped off her mask and made Ririka question her identity, Ririka started following Mary around since then.
Though Mary was annoyed by Ririka, she was the only reason that Ririka came out of her shell and became an independent person and not just someone who could copy Kirari.