Karin serves as the Operator for Katagiri Squad. She's generally pretty grumpy—something that became obvious when Jin showed up at the base and she clearly wasn't thrilled about it. The manga doesn't give much insight into her personality beyond that, though the anime expands on it a bit, showing her genuine annoyance with Jin.
In the third season, she narrates Tamakoma Second's four-way Rank War during Round 7, where they face off against Azuma, Kageura, and Suzunari squads.
Content compiled by AnimeList.moe from publicly available sources.
