The answer in defeating that oldie is probably gonna come from the flashbacks...

Also, I don't know and I don't think the answer on why light cannot counter those oldies disciples dark magic. So here's my theory:

1. They are using shadow as a fuel to resist light. Whenever there is light, any object will have a shadow unless fully illuminated in every direction. So the light magic from Neid and that nerd can't harm that darkness because the light they made also created shadows in which the dark mage spirit or whatsoever is that can absorb.
2. Darkness is the absence of light. So they're probably using dark magic to trigger negative emotions or experiences of the people to extinguish their will or their light. Then those dark mages feed on the darkness that they got from those negative emotions.

The 12th most powerful being in the continent, Ruru in boots.

After all that meat, we got cheddar cheese. Yummm 🧀 🧀 🧀

So we have meatballs, porkchops, and barbeque. Hmm, our mc's cookingggg

Ohh...a meatball.[poco:0]

It would be great if we can have an arc where he teaches cultivation methods to others. Because Earth hunters are kind off weak😁🫶

This is one of those manhwas where I think harem is pretty acceptable, so idk.

That black dome is prolly a reversed infinite tsukoyomi