Noriaki,
Don't listen to these guys telling you how dense you are. From what you've said, it's obvious why she wanted you to lie down with her that night. She liked you and trusted you and knew that you wouldn't react to it in the way a lot of other guys who were just desperate to "get some" would!
As for what you should do now, I don't know. I don't know you or her and that's everything in figuring something like this out. If you don't feel completely ready to let her know how you feel and go for it, then don't. But keep in mind that you shouldn't let just regular old nervousness stop you either. You're gonna have to make the move to start the ball rolling when you're ready to take the chance, because she's already got you and an excellent situation for herself. I don't mean that to sound like I'm saying anything bad about her either. What girl wouldn't want a wonderful, sweet, dependable, and attentive guy with her, not making any demands of her.
As for the tickling thing, it just sounds like an excuse to get you to touch her, and that certainly can't be a bad thing, now can it? Play the game. Tell her you've researched this and found some possible ways to do it. Then, if you're feeling brave, just touch, caress, and kiss away pretending it's all part of the game and see what develops.