Spring Gardens Avenue is lined with Japanese restaurants. It's hard to tell them all apart. Kiyomizu is the last and furthest (east) restaurant from Yonge Street. It's a cozy little restaurant, that serves pretty good food.
The nice thing about this restaurant is that they have a lot of booths and their tables (non booth ones) are all separated, giving each table a somewhat private dining experience. Their service is quite fast, I've never experienced a problem dining here. They have a lot of bento box and combo selections so you're sure to find something you like. I order their veggie bento box, which comes with tempera, rice, salad, soup, a roll and a side dish (different ones, depends on the day). It's more than filling, and reasonable priced!
At lunch time (which is when I'd usually go), it's busy but never to the point where you have to wait for a table. The lunch crowd are usually business workers who work in the corporate towers close by.