Why "Shinigami"?!?
Is that a translation error?
In the Japanese myth of the Shinigami, they usually wield "Yari"... those are spears, not scythes.
The one who is usually depicted with a scythe is the Grim Reaper, and that's the western equivalent to the Shinigami...
Also, did he just instantly grow back his leg, or is it just a momentary magical apparition?
EDIT:
I've Checked the raw...
the word used is "死神", without a doubt, Shinigami.
To make things worst for the mangaka, he even added the Furigana "しにがみ" or Shi-Ni-Ga-Mi, like... spelled out. Funny, a Japanese author misnaming a Japanese deity...