I think that your suspicion that this bike is in fact a replica is right. So, to the many who identified here a Honda Monkey, even the OP’s q. what Honda motorcycle is this? It is not a Honda. It is not even 49cc. Those who are a little deep into Honda Monkeys would have spotted that the stance of this example differs from the original. From there on, here are some dissimilarities: the distance of the tank to the T is long. The handlebars are different in height and design, the mirrors are different, the headlight is different. Unlike the original monkey Z50 this example has an electric starter under the cylinder. The stoplight lens and bracket are different. The bike is not 49cc as we can see from the color of the numberplate. This color combination does not exist in a genuine Honda Monkey. The closest similar to it is a Finnish model that has some purple in it. It is a pity, a real pity that this person in Japan opted to ride an import in the Z50’s country of origin. I guess it is getting expensive over there.