First you will have to cut out your shapes. You will need two body shapes, two claws, six little legs, one seaweed piece, and two white circles. Cut a smaller circle out of one of the white circles.
Start sewing the two body pieces together. You will have to leave an opening at the "bottom" of the crabs body to connect to the sushi. The opening with have to be the same size as the small circle.
Sew the bottom of the crab to the top of the sushi.
Start sewing the whole circle onto the piece of seaweed.
Even out the ends of the seaweed and sew them together. You might need to cut it a bit shorter.
Sew together the top of the sushi to the rest of the sushi.
Start sewing the claws and legs onto the crab body. Now is the time to add any details like googly eyes :)
Stuff the sushi into the bottom of the crab and viola! Now you have made a crab to sushi toy!