Yep, there was a Crayola brand at Toys R Us.  The 
only problem is that the plastic sheet they give 
you to use is a little narrow - only about 1/3 
the width of a regular cel, so I've only tried to 
do small images.  I had to make Sarutobi's sword 
a little shorter to compensate.  However, in the 
package I bought there were two sheets, so I bet 
you could overlap the sheets to make something 
bigger.  They weren't very expensive even in 
Japan - only 1000 yen (less than $10) for a 
single package.  

First you use the black to make an edge - it's a 
thicker paint so it stands up.  Then when it's 
dry you fill in the blank areas with whatever 
color.  You can do color graduation and marbling 
effects and for the colors I didn't have I mixed 
them in a different spot on the sheet and used a 
toothpick to spread it into the areas where I 
needed it.  The "pens" are like a tube of paint 
with a tip.  I didn't try to do any part of the 
cel that was too detailed because the black lines 
have to be a certain thickness to hold the color -
 for example, I didn't bother to do the details 
on Sarutobi's armor.  

I finished the Shimarisu last night, and peeled 
it off this morning.  On that one, I wanted to 
separate colors without a black line between 
them, so I drew a line with the color where I 
wanted the line and let it dry before I tried 
filling in all the colors.  It worked pretty 
well, even though the color line doesn't stand up 
like the black line.  Here's a picture of the 
Shimarisu on my back window.  Good luck!

Jennifer