I do know it is most likely a VFX mesh exported from Blender and the animations are done through the Tween service. However, how would one align the trail based on where the sword swings?
It’s probably just spawned some ways off from the HumanoidRootPart such that it’d match the swinging animation. The crescent doesn’t actually appear until the sword is mostly across the body nearing the end of the animation before it simultaneously rotates and fades quickly.
I feel like you could do your own experimenting to get something you like, matching VFX models to animations. In fact, actually, if you do your animation on Blender you could do animate the effect model too and match it up, just that the rigging should also be done properly for the weapon and the effect itself. The aftereffects (specifically the fade) can then be done in Studio with code.