I believe you misunderstood the question, or maybe I'm biased because that's what I'm wondering about: he asked how he fights with the weapons he eats. Again, I was wondering about the same thing.
If he literally eats the swords as we have seen, how can he physically use them afterwards, or where did he procure such a unique weapon as the needle, especially without any money?
Hello~~~ dear readers, first is the title is sword-devouring *in short he actually eat/devoir the sword, for context his ancestral bloodline have the blood of dwarves. Since you guys are only asking how he ate and use the blades afterward here's a clear summary.
On how he eat the blade, he heat up the blade to soften the blade since it was made on steel eating it directly could cause him internal bleeding, also eating it is painfully hot why? After year of generations the natural fire resistant of the dwarves in there blood disappear that why he cried in agony the first time he devoir an actual blade.
And on how he use the devoured blade, he utilized it by using the memories of the past owners. Ofc there's advantages and disadvantages. Devouring a blade he skipped the actual training on how to wield the weapon itself but the backlash is that he also need to train his stamina.
It like
Eat -> skip sword training -> poor stamina.
Well he also inherited the previous owners stats, the same thing when he devoured petel swords (RIP legend) he became a sword runner.
It's mostly inheriting the previous owners stats and memories and understanding it will* where he could utilized the stats to it exitent.
I hope u understand ( ̄∇ ̄")

Dumb question but if he eats the swords how can he use them? He eats the needle maidens sword but then uses it to fight after that? Im assuming it is manga magic and I am not supposed to think about it haha. Or do the swords disappear when he integrates them fully?
I have cried three times every swords has such a good backstory! Can't wait to see how the story goes.