A fad among children involving sticking koyukkuris on top of a custom-fit top, and seeing whose yukkuri beyblade lasts the longest. The kids playing it usually have the distraught parent yukkuris next to them begging/demanding their children back, but the kids simply ignore them... right until the koyukkuris die (too weak to withstand any more than one go), then they get the parents to refresh and make more.
The story ends with a comment that this activity and the children who play it are supported as they help in exterminating yukkuris.
Marisas are found to be the better yukkuri beyblades, mainly due to their size and toughness being better than the others. Chens are too light, and Patchoulis are... best not considered.
Meh, its an okay idea but the implementation's not so great. What you really want to do is get some hamster balls, a wide open space with pits and traps and let'em roll.