Nemu has not been seen with a zanpakto in either the anime or the manga. However, an artbook titled "All Color But the Black" shows her with a katana. It is unknown where she keeps it, but considering the fact that she is an artificial being, she could be concealing it anyone on or inside her body.
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A: because he hsa an amazing zanpakto that makes him almost unstoppable B: because he has mastered almost every single category (speed, strength exc.)
shikai - zangetsu : really big zanpakuto but not so strong (made by refined steel) bankai - tensa zangetsu : really tiny but can cut trough steel and titanium (made by black diamond) 3rd release - juha getsu : double wielding zanpakuto and stronger than before (made by unknow because it's really new and have seen in latest manga)