Guts has been killing demons with the Dragonslayer for so long that it exists in the astral and the physical world. Meaning he can kill pretty much any supernatural being, including the Puella Magi verse's Witches, with it.
magical middle age guy - I literally spit over that line
Sorry to interrupt. --witches are supposed to be beaten by magical girls.
Why am I even fighting then?
--Where'd he come from? Where's he going?
Is god dead?
Dad, give me a sign. That's for messing up your hunt. --who? What was that?
--A magical girl? No way.
That's clearly a magical middle aged guy.
If I'm being charitable, he's a magical gentlemen.
--was he even using magic?
--Seriously what the hell?