We arrived for dinner at Iki Laboratory after a long day of sightseeing in Sapporo, and they were full. I decided I liked the look of the place, so I made a reservation and we came back a few days later.
The food was good. I had soy-meat Karaage (Japanese style fried 'chicken'), and it was delicious. The servings weren't huge, but the quantity of food was sufficient.
The place had a cosy feel to it. There's not a lot of seating, and it always seemed pretty full, so it may be advisable to book in advance. They do have an English menu, that clearly tells you what dishes are Vegan, but you may have to ask for it, as not all servers seem to know it exists.
If you're looking for Vegan food around Odori Park, this place may be your best bet.