I think it's Miyano Akemi's lost sister. At that time, Minmei seemed to have just been killed by gin. Before Minmei's accident, she sent a short message to Yixiu, saying that she would quit the organization after the task, and asked Yixiu whether she would really associate with her as a girlfriend. As a result, Minmei died. Yixiu decided to avenge Minmei, of course, mainly to destroy this organization, so she cut her hair. Since his girlfriend died, he was naturally dumped. This should be regarded as his self-mockery. In fact, he loves Minmei, otherwise, he wouldn't leave her a message.