To understand the role of Norse mythology in One Piece I think we need to dive deeper. Tyr lost his arm to one of Loki’s children, the beast wolf Fenrir.
This sacrifice had to be made to maintain order. Shanks risks his hand to a Sea King.
Tyr was prophesized to die in the hands of Garmr. IIn Norse mythology, Garmr is a wolf or dog associated with both Hel and Ragnarök, and described as a blood-stained guardian of Hel’s gate.
In many iterations he is known to have three heads.
The fight between Shanks and Blackbeard has been hinted a lot. Those Shanks’ scars, Shanks’ concern about Blackbeard’s rising strength, Blackbeard outright saying at the end of the War of the Best that it’s not the time for their fight implying there will be one.
So the ending of One Piece could be based off these events.
*Theory by luffyintherange