You and Mei were fighting someone until the point the foe realized they weren't going to win. They made an attempt to retreat, however—

before they escaped, they had caused a large roof tile to fall off from a near building, and it hit Mei square in the head…

"Ooowww— wha–! Hey, get back here, you little-! little jerk…"

her words faltered a bit as they slurred together… Oh, this girl is concussed…