I'm amazed that Yajin hoped to find the mirage fox's body where he had left it; there's no way other monsters wouldn't have found the corpse and started snacking. I don't know why he'd even think that another adventurer would find it since there shouldn't be that many adventurers roaming deep in the forest and, even at higher levels, shouldn't really be able to track corpses by smell like many monsters would (from what we saw there are packs of wolves going around).
I'm sure Yajin was doing his due diligence and checking for other presences, but mirage foxes sure are tough to deal with thanks to their presence concealing skill. Still, it was a stroke of luck that the fox decided to move the body to a different location, because it alerted Yajin that something was wrong and I guess it prevented him from actually losing an eye.
It's clear now that the mirage fox he killed previously was a cub - it was really small - so it's quite surprising he managed to avoid the parent then. (Reading back that chapter, I still don't understand why he thought going in water would get the ants off him; I'm pretty sure pockets of air would naturally form around the ants and could sustain them for a lot longer than he could stay underwater.)
I wonder why the mirage fox moved its child's corpse to a different location. If the corpse was still there, Yajin would not have been alerted and instead would have dropped his guard for a moment (brain automatically tunnel visions on something of importance). I guess it's probably because the corpse would have long been desecrated by other monsters.
I wonder what it did with the corpse. Either eat it or bury it I guess.
It's pretty cool that the adult mirage fox can use magic; I wonder if it'll get Yakin interested in that.