[It absolutely is for a spell, and to lessen the price he has to ask for whenever Shura goes about making her wish. Because he's pretty sure Shura wouldn't accept a wish at full price, so getting some of it paid off ahead of time seems like a good idea.]

If you say so.

[After a pause, he adds:]

I did forsee your arrival, but that was only one of many possible futures. If you truly do not wish to return, you won't. If you choose to return, then you will. But either way, it will be of your choosing. The futures I see are not set in stone. Anything can be changed.

[A few words to be reassuring, perhaps. Shura did seem bothered by how much Watanuki knew. Maybe he should explain that as well? Except knowledge comes with a cost as well, and hearing who told him some of the stuff he knows probably will upset her.]