I just came to say that I've been thinking about this story while writing The Novel's Extra.
I've seen the latest chapters of the One Piece manga, and supposedly Shanks and Shamrock would represent Hati and Skoll respectively.
I also keep thinking that possibly Loki has the Devil Fruit of Fenrir, but I'll have to see about that later… if I ever get to that part of the story.
So that's where I'll decide whether to go with the alternative of Garm or give him another option in that case.
At one point, I thought about abandoning this story to make another one where the protagonist had Boa Hancock as his wife and also started sailing the seas, fighting and forming his own crew. But I left it aside because I didn't see much potential in it, and because this story already has many chapters.
And that would be all.