It's this little tiny hole in the wall place on Takeshita Dori in Harajuku. You get off the Yamanote line from the Takeshite Dori exit and walk down Takeshita Dori.  Cross Meji Dori (a big street) and it's about another minute on your right.

Like the ad said, everything on the menu features kabocha. We opted for a course menu so we could try more things

pumpkin lasagna

pumpkin doria

pumpkin dessert

We got a kabocha salad followed by kabocha lasagna, kabocha doria which is a casserole like dish, this one served in half a kabocha and finally we got 3 desserts made with kabocha.

All in all it was good and it was certainly fun.