Junko's plan in LoLK was to use fairies, who were purified into "pure impurities" to storm the lunar capital, as the Lunar capital's residents physically cannot get to close without becoming irreversibly impure and thus unfit for the lunar capital. This is just that playing out on a one-to-one scale.
Imagine tag but you get banished from your home if you get caught. That's Sagume right now.
