Mix together mayonnaise and wasabi. Set aside.
Place a sheet of plastic wrap a little bit larger than nori leaf (dried seaweed sheet) on your working surface. Lay your nori leaf (dried seaweed sheet) on an angle with a corner pointing up (in a diamond shape) with the non-shiny side facing up and the shiny side facing down.
Place about ½ cup cooked rice into a thin layer shaped into a square in the middle of the nori leaf (dried seaweed). (Wet your fingers with a little rice vinegar to prevent the rice from sticking to your fingers, if you wish)
Place 3 slices of imitation crab meat (or real steamed crab meat) in an even layer across the top of the cooked rice, which is lying on top of the dried seaweed sheet. Press down slightly with your fingers. Drizzle ⅛ cup of wasabi mayo on top of crabmeat.
Place a thin layer of sliced cucumbers and then thin layer of sliced Japanese daikon pickles (or maybe a fried egg instead for that bright yellow color) on top of the crab layer.
Layer on top about ½ cup of cooked Japanese short grain rice and shape flat and into a square. Press down slightly.
Take note of which way your ingredients are laid out before you fold up your onigirazu. (The goal is to cut your wasabi mayo crab onigirazu so that you see a pretty cross cut of your sandwich displaying all of the colorful fillings) Gently fold up to opposite ends of nori leaf up and around the sides of the onigirazu so the points or the ends of the nori leaf cross at the top. Then take the other edge of the nori leaf and gently pull up the other two sides and cross until the edges meet up at the top. Place the toothpick in the direction (just gently lay on top as a reference tool) that you will be cutting the onigirazu to show case the ingredient layers. Finally, wrap the wasabi mayo crab onigirazu firmly and tightly with the plastic wrap and place in the refrigerator until ready to serve or at least 30 minutes.
Remove the plastic wrap. Wet your sharp knife with water or rice vinegar (to make it easier to cut) and cut your wasabi mayo crab onigirazu in the same direction of your toothpick marker. Place your delicious wasabi mayo crab onigirazu into your bento box with other treats and enjoy on your next picnic or work/school lunches. Enjoy!