If I were to make a minor complaint about some veg cafes in Tokyo, it would be that many dishes are similar and not as unique or creative as in other cities with a more developed veg culture such as Taipei or San Francisco. In that respect, Ko-so Cafe truly is a treasure! The concept behind the restaurant is that they use their own, homemade ingredient called kōso (酵素 lit. "enzyme") as a base for nearly every sauce on the menu. Rich in umami (savoriness), kōso is made from a blend of 88 different ingredients that are then fermented and aged for 18 months.
I went on a weeknight and started with the nut pâté & olive paste salad for an appetizer. The veggies looked beautiful and it was topped with fresh alfalfa sprouts, nuts, and vegan cheese. The waitress then appeared with tiny pitchers of 3 different homemade dressings to try: celery, red pepper, and onion. Each 1 contained only kōso and vegetables and the flavor was excellent. The salad also came with 2 slides of brown focaccia bread with some kuromitsu (lit. 'black honey', vegan and made from unrefined Okinawan black sugar) for dipping. Not everyone will be a fan of the sweet dipping sauce as it's typically used for desserts but I enjoyed it. For my main, I ordered the soy milk ricotta cheese & basilico romagna pasta. It was excellent, full of flavor, and the noodles were done to al dente perfection. I also found the portions of my salad and pasta to be generous by Tokyo standards. Overall, I had a great experience at Ko-so Cafe and my only regret is that I didn't try it sooner. Highly recommended!