Cocolia was Bronya's mother, who has been brainwashing her since she was a child, she didn't allow Bronya to go to the Undercity, as she said it was full of evil people. Even thats not true, which made Bronya enemies with the Undercity people, but she didn't mean it. Her mother was brainwashing her, which made the Undercity people mad and told Bronya that her mother isn't telling the truth, mother was turned out to be the villain

Bronya and Seele (the leader of the Undercity people) we're forced to fight Cocolia, Bronya didn't want to but she had no choice, her mother was the evil one after all, she had been brainwashed since child

at the end, Cocolia lost the battle as she dropped to the groud, she started to turn into ashes that blown in the wind