The amount of rice you need is 150-160 g, or a little less than one large, loosely-packed rice bowl. For reference, 1 rice cooker cup worth of cooked rice usually weighs around 350 g.
For each 160 g of rice, mix in 1/4 teaspoon of salt. I'm using 4 bowls of rice, which will fill one large or two medium bento boxes, so I'm adding 1 teaspoon salt.
Pack some of the rice into the bento box. Don't make a right angle between the edge of the rice and the bottom of the bento. The edge of the layer of rice should be slanted to make the stripe effect look better.
Slice each strip of nori seaweed to the length of the outer edge of the rice. If the strips are too short, just add an extra piece to the end.
Keep on packing in layers of rice, followed by strips of seaweed. Keep pressing the mixture away from you to secure everything in place and achieve a more defined pattern.
The pink in the bento is "Cooked Tarako in the Microwave" Recipe ID: 2091181.
Story Behind this Recipe
I had a day where I didn't put any effort into any bento side dishes at all, so I thought that I should at least try to do something special with the rice. Ultimately, this is just a nori and rice bento.
Pack the rice in so that the edges are slanted!
When adding the salt, make sure to sprinkle it over the rice evenly. Whoever eats the bento shouldn't be able to see it!
If you like a stronger flavour, then increase the amount of salt.
Once you get a feel for how much salt works best for you, it becomes easier to whip up large amounts of onigiri for big events since you won't have to salt every separate batch.