Carrying a passenger on a scooter reduces performance, makes cornering tricky and looks ridiculous. Leave it to the Japanese to turn it into a competitive sport.
This event is called the Osu Rider's Cup and it appears to take place several times a year on a go-kart track. Don't be fooled by the relatively slow speeds, getting the most out of a CVT-equipped scooter while hauling double the usual weight is an incredibly tricky task. Making things worse, that extra weight is tall and tends to move around behind you. It also extends the front suspension which makes steering slow and imprecise and makes front end washouts not just likely, but inevitable. The passenger also compresses the rear and adds too much weight for the damping to cope with, meaning the rear end will wobble around on over-compressed springs with very little control.