Shisui isn't keen on swooping down on their 'meeting'. Instead, perched on a vantage point, sharingan on, he records everything. And since he's also lip-reading, happens to learn quite a bit about his student. ...And the other person. He's known about their correspondence after he'd spoken to her about it, and hasn't brought it up since. So this? This was a long time coming.

Carry on, you two.

Not that he's in the least pleased about it.