Oh good, I get to try out some of the things I've been thinking about.
First page: Basically the boy has bet his older sister that if he beats her then he gets to tie her up and tickle her for 30 minutes, so as you can see he wins at the game and ties her up as per the bet.
Second page: She calls him a pervert (naturally since he's taking off his sister's clothing) and then he says he's going to tickle her for the remaining 15 minutes like that. Sister thinks "Oh god I didn't think it would be this bad to get tickled for 30 minutes!"
Third page: More of the same. Most of this is the "ahahahaha oh god stop please" sort of thing you'd imagine it would be. Brother mentions there's 10 minutes left, and that tickling is sister is fun, especially when she can't get away.
Fourth page: "Oh god, I'll do anything please just stop" et cetera. Finally he stops, the brother asks if she'd been crying, apparently feels a little bad about what he's done. Then she says it's okay, asks him if he wants anything, and he answers that his dream is to take a bath with his sister, the results of which you can see for yourself.
That's basically the gist of it.
