@Yurisivel No, it is based on a light novel.
Also, as far as I have read,
there is no harem or romance to be seen.
The story is good but very repetitive since it keeps repeating the same formular:
1. MC makes friends/allies.
2. Evil people kill friends/allies.
3. MC uses the death of friends/allies as an excuse to slaughter the entire country from which evil people came from.
4. MC makes new friends/allies and the circle repeats.
I forgot about this, since I don't know anyone else who reads them.
If you can pick up the LN, you might as well. They're pretty light, even among light novels.
Ah that's a shame. Though I guess I shouldn't be surprised since the author is the same who wrote the Modern Firepower Villainess novel. I guess I'll just keep reading this until I get bored or sick of it.