Shikkaku Mon no Saikyou Kenja~ Sekai Saikyou no Kenja ga Sarani Tsuyoku Naru Tameni Tenseishimashita~ - Chapter 183 Strongest Sage, Watches Over Negotiation

... this type."

On top of being small, parasite monsters put around 30 types of concealment magic on themselves so it's quite difficult to spot one.

Thus, these monsters can stage a come back no matter how many time you crush the host as long as there are other monsters around to be their next host.

It's gotten to the point that there were cases of countries getting dangerously close to fall by a single parasite monster in my past life.

"This little thing was the one ...