Very nice! I like the progression of their relationship here. It feels unhurried and natural, and gives the impression of real people in a relationship--it all doesn't happen at once--in spite of the extraordinary circumstances they have to deal with in their jobs.

When though Ada's not our point of view character, we get a sense of who she is through the details you use--the lipstick kisses, the butterfly tattoo, the fact that she takes off but leaves him a pot of coffee. Little hints that speak to much more.

And the end is really cute, quite fitting. She's independent, like a cat, not the kind of woman who can be rushed or pressured into anything. But when she decides what she wants, well, it's all over, heh.

Nice portrayal of Leon throughout--I liked the contrast of quiet competence at his job, and inexperience with relationships. Very believable. And this was just lovely:

he kissed her and invited her to his hotel room, hoping his voice didn't betray the pounding of his heart.

Anyway, nice "fill in the gaps" sort of fic--I've always liked the vibe between these two. Nice to see you run with this, since there's just so much potential there!