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So, there are multiple interpretations of Nika; a liberator, a destroyer, a god who laughs... etc. Of course, the "true" sun god (if there is one) will be proven to be Nika the liberator, which is the fruit Luffy possesses right now. But DFs are the manifestations of desire and born in response to people's wishes. If enough people want Nika "the destroyer," like that one giant speaking up, then it will come into existence, just like any mythical zoan based on legends.
Which brings us to the subject of Loki.
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Seem familiar? That's because Loki is doing the exact same pose Luffy does in G5.
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This serves two purposes.
1- Obvious foreshadowing for Loki as a dark parallel to Luffy/Nika
2- Shows that Loki is pretty knowledgeable on Nika, to the point he can perfectly copy his signature pose.
And with this in mind...
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Loki thinks of himself first and foremost, as the Sun God. Since Loki's fruit was a prized possession of Elbaf, it's either from proper Norse mythology or Elbaf's own religion. Look at the contenders from Norse Mythology.
Fenris and Jormungandr are destroyers, but don't have anything to do with the sun, or really have a related theme going for them. So, there's not really a reason for Loki to think he's a sun god based on having those fruits. Surtur is more likely, given he's a fire giant who burns everything down in Ragnarok, but I think "Destroyer Nika" is far more likely in the context of the larger story.
1- Loki copied the exact same pose Luffy does when he's in G5. This already implies he's actually pretty knowledgeable of the Nika/Sun God legend and what it entails. Nika is his homeland's myth after all. So, in order for him to loudly proclaim he's that mythical sun god, he must be as close as possible to the real thing to believe it.
^Nika as seen by Elbaf.
2- Nor does Oda have any issue including other Nikas into the story, looking at Bonney's transformation with the Nika fruit. This may even be his way of backtracking from making Luffy too special in the scheme of things. In an arc like Elbaf, some sort of victory over Loki might be what's needed for the giants to give their full allegiance.
Personally, I wouldn't like Loki to transform into another nika reskin, but it seems like the story might be pointing toward it. I hope if this is true, his zoan transformation will have monstrous features from the original myth being distorted. Thoughts?