These are the tools I used. From the left: a nori punch, scissors, tweezers and a toothpick.
Mix the mentsuyu sauce and a little salt in the rice.
Put half the rice on a piece of plastic film and make a chestnut shape.
Cut the nori seaweed to fit the size of the onigiri. The left side piece cut to cover the whole bottom, and the right side piece is cut to cover the front part of the bottom only. Use whichever cut you like.
Make the face parts by cutting them out of the nori seaweed, stick them on and the onigiri are done. If you cut a slit on both sides of the nori a little, it is easier to stick on. The blushing cheeks are made with ketchup.
Story Behind this Recipe
I used to cover the bottom of the onigiri with black sesame seeds, but that wasn't working too well, so I changed to using nori seaweed. It looks like a chestnut now, so I uploaded the recipe.
When shaping the onigiri, make the top pointy and the bottom round and fat to make it look like a chestnut. Cut the nori seaweed in whichever way you like in Step 4. Small children may find a big piece of nori hard to eat, so I recommend a smaller onigiri made with the nori on the right.