Portal invasion type novel. Mc is OP, laying low etc.etc. 

The translation is quite awkward at times. And filled with inconsistancies.

Monster with 20k hp taking 10+ 5k damage hits to kill.

All hits dealing the same damage for some reason.

Mc oneshots something but the fight taking minutes.

Portals started to appear 2 years ago but only older people are strong.

We need more people to deal with these lvl 3 rifts. Then 10 chapters later there are multiple lvl 5 rifts on farm.

Etc.

Its a bit of a mess. Nothing revolutionary in any way.