Hmmn...
Not sure how Oda's going to justify this DF being able to kill immortals but that seems to be the implication atm.
Will also explain why Rocks named it a requirement in order to overthrow the WG and why Harald immediately told Loki to eat it as a means of stopping him

Could it be hades related lol? will also somewhat fit with the ice theme given the correlation btw the underworld and cold in this series.