The Sun Pirates reference is obvious since this was revealed in the recent Jinbe fight.
The Sun Pirates crest is a sun of course. The idea was from Fisher Tiger and is branded over a claw of the Celestial Dragons branding.
Nika’s title of “Sun God” probably ties in with all the sun motifs and references we’ve seen throughout the series, especially with Alabasta, Shandorians, Kozuki Family and the Sun Pirates.
Many fans claim that the silhouette of Nika looks like a Shandian.
The silhouette of Sun God Nika looks eerily similar to the silhouette of Luffy dancing in Skypiea Arc. There are two such chapters. One would be Chapter 253 where Luffy, Usopp and the wolves were dancing around the campire with Robin looking at them while sitting on a rock.
The other woud be Chapter 300 where Luffy and the Straw Hats are partying with the Shandorians and the Skypieans around a huge bonfire after Enel is defeated.
From Chapter 287. This is referring to the Giant Snake but his name may be a reference to Nika.
Another reference to the sun: the Elbaf denizens believed in offering their thanks to the sun, by fasting for 12 days before a great feast, a tradition known as the Winter Solstice Festival.
The Thousand Sunny reference: Luffy’s ship has a sun as the figurehead. Feels like a stretch but…
The sun is what brings the Dawn. So basically the sun is what follows the break of Dawn. According to Pedro’s statement, he believed the Straw Hats would bring about the Dawn.