If you're in Tokyo, the trails along the Tamagawa are fun to ride for day-trips. There are paved trails (with a few gravel bits) going pretty far north, and then, if you want to see how things go on steeper stuff, you can get on roads and do the killer climb up to Okutamako if you want to go further.
This trip is an out-and-back about 80km each way, 160km total, but you could do something like this and break it up into a couple days. If you go a teensy bit further than shown on the map you could put your foot over the line into Yamanashi-ken
Not a fan of the sweet stuff, but you nailed it with the yakisoba and takoyaki. Them and beer are where it’s at.