First, after you gather all your materials, cut out two semi-circled shaped peices from some old newspaper.
This creates the pattern needed.
Trace around this pattern, leaving about an inch allowance.
Cut out the two peices.
<-- should look a little like this.
Lay the peices together so that the good, non-drawn on side is facing each other.
Now pinaround the shape, leaving a section unsewn so we can flip it good-side out after sewing.
The unpinned side prefferably should be in the middle of the bottom side - this is so that the sewn up outside seam will be hidden by the peices of nori/seadweed.
Sew it all up, except the area we left unpinned.
After it's all sewn up, flip it good-side outside. The seams should be hidden inside.
Now, stuff the pillow full of toy stuffing. You can get this stuff in most craft, sewing or hoddy stores.
When it's all stuffed hand sew up the open bit. It's okay if it's messy - the nori/seaweed will cover it up.
Now, the seaweed is made from a rectangle peice of black material. This peices' size depends on the size of your onigiri.
Cut the peice out and pin down the raw edges. Then sew them suckers down.
You should have two peices like this.
Now glue your nori/seaweed onto the riceball.
Look before gluing so it's relatively even.
Add some eyes, some cheek and whatever you want.
Ta-Da! now you've created your own cute onigir pillow.