Eating in Tokyo solo? Casual But Good

I'll be solo in Tokyo for 4.5 days in April (Female, 55 years old), and I love good food... but I don't like eating in fancy restaurants alone. In a more casual restaurant I don't mind dining alone, watching people interspersed with reading on my phone, but in a fancy restaurant, people watching is more intrusive and I feel particularly out of place.

Does anyone have suggestions for any particular places I should eat (any meal, not just dinner) - casual and welcoming to solos, but with particularly good food? I will be staying near Tokyo Station at Hotel Ryumeikan, but I'm not entirely sure what I'll be doing or where I'll be going during my days, which means I'm pretty flexible. My usual routine when traveling is to wander around a bit and look for places that look popular and interesting, even if I have to manage with hand signals because I don't speak the language - that's usually served me well so far in my travels. But, with the Chowhound wealth of knowledge, I thought I'd ask for any particular suggestions.