This is really simple to make. Boil an egg.
Surely you know how to hardboil an egg, right? Just
in case, heat some water - enough to cover the eggs,
little more than that - up to a boil, gently put the
eggs in with a spoon, and let them simmer for about 15 minutes. Then
get a bowl of cold water and put the eggs in there.
This not only stops the cooking but creates a layer
of steam between the egg and its shell, which will make
it much easier to peel.
Now for the soy part. This is really complex. Peel
the eggs, put them in a cup or bowl or whatever the
smallest container that will hold them is, and cover
them with soy sauce. Let them soak for an hour or so,
depending on how strong you want the flavor. If the
soy doesn't cover them completely, or they're pressed
together, rotate them a few times for even coverage.
When you take them out they will have turned a tan color
from the absorbed soy sauce.
For those into special effects, roll the unpeeled
egg on a hard surface, pressing it down to crackle the
shell, but don't peel it. Make sure it's crackled all
over. Then soak it in the soy just as it is for a few
hours. The egg inside will be mottled instead of an
even tan color. The cracks will be outlined more sharply
on the egg if, after you boil it, you don't immerse
it in cold water and thus create a space between the
egg and the shell for the soy to flow around in.
If you are bored with the usual egg-shape, you can buy egg molds to make hearts, stars, et cetera. Just peel the egg while it's hot, smush it into the mold, then let it cool. Presto, weirdly-shaped boiled egg! I bought my mold from The Bento Store on eBay.