Xie Yun isn't sure who the man is. All he knows is that the man looks a lot like his not-twin, Lan Wangji. He also notices that Lan Xichen's sword gleams just right when it strikes those that were coming out of the water. However, the young emperor wouldn't let the other fight alone.

So, wielding his own sword (he's yet to name the gleaming beauty that's more beautiful than himself) he cuts down the creatures coming from the water. Hopefully the creatures wouldn't drag himself or this stranger into the water. They, at least, wouldn't touch this other man if he could help it.

"You have wonderful sword form."