is it the one you get around mission 8? cause it said that the rank 5 blade was unlocked but I couldn't upgrade it anymore, and I'd rather have the other one back

That's the one, and it's broken. The absurd health-drain I could deal with, but the damage frames just defeats any purpose and fun you might have using it. Get the level 5 claymore, best weapon in the game anyway.

Yeah, I've been collecting the stuff and am on my way to getting it right now actually, then I just gotta get the rank 5 dual knives, I can't remember what they're called though