Pack the rice into the bento box and cover it with plastic wrap to prevent it from drying out. Set aside to cool.
Cut the mouth out of nori. The size of the mouth should match the size of the bento box. It will be easier to balance the facial features if you cut the mouth slightly over-sized. (The nori will shrink so it's fine if the mouth is wider than the bento box for now.)
Once the mouth is done, use the size of the mouth as a guide for how big to cut the eyes.
Cut the eyes out of sliced cheese and attach all of the facial features (if they don't stick, feel free to use mayo as a glue). And you're done!