Due to Marisa's influence (delusion), the kos now don't scare humans (bikes) anymore, so they're just going and challenging every single human they meet. Bad luck for them, the humans didn't even give a fuck so they just rolled over them, effectively killing every delusion kos that thinks they can match human. The clan's kos now have been wiped out, so they decided to punish/direct their anger at the "culprit" that brought the clan to its doom.