"He does stuff with water." What exactly 'stuff' involved, well, Link didn't explain. In fact as far as he's concerned, he's already imported more than enough information; Mikumo does stuff with water, Rokuro does stuff with water, and now she can go off and do whatever it is she wants to do with this information.

As she starts to speed up then, he does too - except not exactly in the same direction. Mikumo's going one way, but Link's spotted another group of drones on the horizon and started moving towards them, fast. Which means he's not exactly keeping track of Mikumo anymore, and is starting to leave her behind.

(But well, she's doing okay. She can kill drones with water. She'll be okay while Link goes and deals with this, right?)