Tf you mean this is faithful adaptation? I thought they only take the sword's name and not their story
Additional content aside (Lynn herself, Gender bending/major emphasis on the fantasy, the fetishism and some secondary characters like the persian team but there is more) this story so far has been faithful to the OG. If that's true then
While it has different versions of the original Rosengarten, we can just agree that this is pretty much an cracked versions of the german myths put into a manga.
Props to the mangaka and the writer to create something that somehow is both faitful and absolutely absurdly hilarious to read.