Despite the name, warabimochi does not actually contain any
mochi; instead, the base of the "dough" (for lack of a better word)
is bracken flour (jp. warabiko) and sugar. The primarily resemblance to mochi
comes from the fact that like mochi, the dough is almost entirely
tasteless by itself.
There are several variations on the formula, with rather different
results. The form commonly sold in Japanese convenience stores during
the summer is refrigerated and contains moist, translucent balls of
warabimochi. To eat, you pour the thick black mitsu
syrup on top, stab a ball with the included little pick, roll it around in
kinako flour and devour with relish. This, in fact, is the
very dish that turned me into a wagashi fanatic; see homemade warabimochi for an exceedingly impractical recipe.
The more classical (but in my humble opinion far duller) form
has the syrup mixed into the dough itself, turning it into a brown mess.
It has already been rolled in kinako for you, and there it
sits in the gift shop, packed with preservatives and slowly turning
gummy and tasteless. Yuck.