Isekai Kaeri no Arafoo Ryman, 17-sai no Koro ni Modotte Musou Suru - Vol. 2 Ch. 6

[VladDracul2]

It's like any other demonic possession story in that regard. Even if they can't stop them permanently, they can keep them from killing more people by constantly sending them back. So, it's not meaningless. They're keeping them in check.

You're right, though that it's an endless war...unless he can destroy their souls or trap them.

Ah, grimdark, my favourite