Set one sheet of nori aside, intact, and tear the other five into small pieces. They don't need to be exact! Set aside.
In a large soup pot over medium heat, melt the butter. When the butter is melted, add the marshmallows. Stir until the marshmallows are completely melted, then stir in the vanilla and turn off the heat.
Add the cereal, then the nori, and mix everything together. Try to distribute the nori somewhat evenly, so it doesn't clump! (If this means mixing the cereal and the nori together before adding it to the marshmallow mixture, do that!).
When everything is mixed together, firmly press it into your prepared pan using a buttered spatula. When it's pressed and flat, lay the final nori sheet over the top and press firmly.
Let the bars cool for at least an hour (or 30 minutes in the fridge/freezer).
Enjoy!
Recipe by The Kitchen Paper at http://c02.ddd.mwp.accessdomain.com/nori-rice-krispie-treats/