If I was a spy I think it would have been smarter to weasel my way in before nightfall, but if it makes you feel better—

[Playfully she reaches out to Gray. Her fingers curled inward except for one. Her pinkie. Outstretched and offering.]

We can promise like this. How about that?

[A childish gesture, maybe, but maybe asking someone to promise to be honest about being a spy when the alternative is getting thrown back to the monsters is childish. Either way, Tohsaka doesn't mean it mockingly or maliciously. In fact she's charmed by Gray's request.]