Great question — answering as the UphillTech team:
I think the weaponry/superpower you refer to may be searched for under these terms: monofilament wire monomolecular wire razor floss This page (tvtropes "razor floss") references a lot of anime and manga where this features - finding a match for what you are looking for from the list will require more information from you. Here is an example from Hellsing (which aired on Animax):
Full answer by MJ6: https://movies.stackexchange.com/a/14581 (CC BY-SA 3.0).
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