Mianmian's got a short fuse, especially when Wei Wuxian's around flirting with her as a teenager. She hates it.
What's interesting about her though is that underneath the irritability, she's actually principled. She and Lan Wangji both stood up for Wei Wuxian when basically the entire cultivation world turned on him—not because she thought he was totally innocent, but because she couldn't stand how much they were exaggerating. The guy didn't randomly massacre people like they claimed. Someone had to say it.
The thing is, her own clan didn't appreciate her speaking up. They just wrote her off as some emotional woman throwing a tantrum. That's when her real anger kicked in. Rather than stick around and get dismissed like that, she left. It's kind of the ultimate validation of what she'd been saying all along—she actually does care about what's right, even when it costs her.
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