How fancy, how long do you want to stay? It's a bit difficult to make recommendations. You'll find some options in Ueno station, some inside the paid area. There is a pretty good burger place nearby called andra. Quite crowded usually. Otherwise, ameyayokocho is nearby, mostly with Japanese restaurants but some other options as well, similar situation in Asakusa. Lots of tourists around there and sometimes hard to get a seat, but easier if you're alone and fine with sitting at the counter
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Somewhere casual as I'll be alone. I'll probably just be eating and going unless they also have decent drinks. I know plenty of places in Ameyokocho will be open, but there really isn't anything there that I couldn't get in Aichi, so I'm more interested in non-Japanese. As I stumbled upon the South Indian restaurant last year, I suspect there might be some other foreign-staffed restaurants that don't close as their families aren't in Japan, so I thought I'd ask on the off chance that anyone knows about any others.
Andra looks nice. I'll probably check it out when I'm in Ueno.
Also, does anyone know any good sites for finding restaurants that aren't user generated? I find Gurunavi and Tabelog overwhelming, and also lacking in detail for individual restaurants. Is there anywhere with more detailed and curated content. I like bento.com despite it's design language being stuck in the early 2000s. Is there anything like that but in Japanese and more extensive?