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longsword

Sword with a thin blade inlayed with ruins. it glowes a soft blue-white hue

looks like metal, created from the souls of the dead

depends on who's holding it. To grimm3 its always the right wheight. to anyone else it would be like wielding a weak feather or an provesional wrestler

somewhere during Grimm3's 4th stage

Its ability to cut is similar to a vorpal blade when it comes to living victims, it does not break as long as there are souls to repair it, Grimm3 can use it to rip out someones soul

The blade is quite literally an expansion of Grimm3's body and falls under the same curse that allows her to recreate a new body.
Grimm3 would rather have a scythe to swing around but the empire decided that wouldn't do the public state of mind any good