It starts as a distant series of distorted notes, carried on the wind through Tokyo’s suburbs. Gradually, it comes closer and the noise builds. Eventually, the van rounds a corner and I am subjected to the full power of a sound system that would not be out of place at a rock concert. Flags flutter from the rear of the white van, which has its party affiliation emblazoned across the bonnet and down both sides. A man in a baseball cap declaring his political preference is behind the wheel and...