A while back I located an amazing place to get a rice bowl topped with some sashimi. This little shop has no seats and is purely take-away, but it’s also only 5-10 minutes walk from our apartment, making not seating no problem.
The quality of the sushi is generally AMAZING (there was one time that I found a shrimp that looked a bit iffy, but that was the exception and the rest of the bowl was beyond delicious). For sushi, one way that I “test” a restaurant is that I will purposefully order something I usually hate, such as ikura (Salmon roe) or uni (sea urchin); if I find that the thing I typically hate tastes good, then this place is good. In this instance, the ikura was so fresh and amazing, it was almost more sweet than salty.
Also, each bowl is made to order, which means you can also sometimes request other items; one example of this is when I substituted flying fish roe for the usual salmon roe in the negitoro kani ikuradon. Being one of their few gaijin customers, when I came back a few weeks later and did not substitute it again, the cashier asked me if that was ok or if I needed make the substitution, which was a really interesting experience. You can get regular status at a place pretty quickly in Japan as long as you look different enough and aren’t in a place popular with foreigners.