the string on the handle for base form is so that u can swing it around and be like scorpion from mortal combat

gabriel u prob dont know what a bankai is but make one and reply out ur idea:
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+Base Form - Katana with string attatched to the handle
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-Shikai - Katana becomes just a handle but it can shoot out the sword like a grapple hook/harpoon
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+Bankai - Handle becomes 2 gloves that can summon controllable strings for all fingers, seeminglessly able to cut through concrete all around + make walls of string