The lava monsters are the typical ones back from Rhash's previous world. No matter how many times you attack them, they would not die unless you destroy their core located in their chest part that is protected by a durable piece of rock
Destroying those cores is the only way to kill these lava monsters. If not, even if their whole bodies were destroyed except for their core, they would still regenerate
That's how troublesome these creatures were
"Go become my cannon fodder and I'll attack from behind" Rhash ordered to his little spider slave
He could only use Khaknur as his meatshield if he don't want a certain someone to scold him
"Hmm? That's weird. From what I can recall, it's big brother that likes being attacked from behind" Reif 'rudely' commented and the newly made arrow in Rhash's hands flickered as he momentarily lose control over his magic