I was so fortunate to be able to eat here. It's not as hard to find as it's made out to be. Just exit out of Exit 6 from Maruyama Koen subway station and turn right - walk about four block - crossing one substantially-sized street, then make a right. Halfway down that little block on the left is a sort of alley/street. Make a left into that alley and you'll see the restaurant more than halfway down the alley on the left.
Food is fantastic and the owner / chef is kind and speaks English. I had set menu which had a sort of tofu - so just adequate in the protein department - could have done with more vegan protein. He sells vegan ice cream! The only place I've seen in Japan with it outside of Tokyo.
Definitely don't put off going here. It's near a great park and large Shinto shrine complex in Maruyama Park. To go to the park just back track towards the trees the opposite direction out of Exit 6 from Maruyama Station (make a left instead of a right out of the exit).Pros: Fantastic food, kind owner, vegan ice cream
Cons: could do with more vegan protein (tofu) in set men, not cheap but not expensive