He ran off after seeing the love of his life show off her incredible grace by falling off the roof.
Is there anything Lan can do competently? I'll admit it is somewhat amusing that both she and Muginami possess the opposite of what their appearances would typically lead one to believe (that the skinny and fit girl would be highly skilled, while the pretty ditz with the large tits would be a klutz). But there has to be something she's actually good at.