You're not going to find a huge high-rise right next to a bunch of row homes; there's rules against that. High-rises have to have a certain amount of space aro

You're not going to find a huge high-rise right next to a bunch of row homes; there's rules against that. High-rises have to have a certain amount of space around them anyway, but also there's rules about how much you're allowed to block your neighbors' sunlight. Basically, making taller buildings is allowed, but they can only be so much taller than the surrounding buildings. Over time, this means things could get very tall, but not quickly. As for unified styles, there's no laws about that AFAIK. They're probably just like that because the landowners want it that way. Lots of stuff in Japan is done (or not done) without any formal laws or rules, but rather because of social pressure and consensus. It's possible that some very unique or culturally-important districts do have certain rules though, which is why I wrote "... in most of Japan".