There was literally a "sun god" in Skypiea blud, and they danced with the same drum sound than the drums of liberation.
Evolution of Luffy's laugh. Luffy smiles a lot but the SFX actually evolves over time. During chapter 1, it went from Haaaa (はーっ) to Shishishishi (しししし) pre-devil fruit to Nihi (にひ) post devil fruit, then to Ni (にっ) post his growth.
Luffy smiles with Nii (にいっ) during significant moments
Oda's wordplay on Nii (にいっ) actually symbolizes Nika (にか)?
Because Oda likes wordplay, what if you put っon top of い to get か. Suddenly Nii (にいっ) becomes Nika (にか)!? It definitely feels like Devi's fruit meaningfully changed Luffy's smile and Nika side of Luffy started to show more, especially during moments of significance. Ok, I know this still feels like a stretch to say that Oda planned for Nika since the beginning. but, wait, there's more.
Nika and Luffy's birthday (5/5). It's pretty well-known that Oda likes Japanese number based puns, which is why Nami's birthday is 7/3 (Na = 7 and Mi = 3) or Sanji's birthday is 3/2 (San=3 and Ji = 2). So why is Luffy's birthday 5/5 (SBS from chapter 130)? A lot of people were puzzled at the time. Shouldn't it be 5/6 since he's Gomu-gomu (Go=5 and Mu=6)? Yes yes, 5/5 is the official Japanese Children's Day and Luffy's like a child (and Usopp's birthday is 4/1 so that could make sense), BUT in retrospect, 5/5 is also 五/五 (remember, Japanese uses Chinese characters also) and as many Japanese readers have been pointing out, 五 is actually what you get if you put ニ and カ right on top of each other. So Luffy's birthday is Nika-Nika. Just to make this point a bit more convincing, remember Rodger's bounty is 5,564,800,000 bellies, which is 55億6480万. 6480 is a pretty straightforward wordplay on Rodger or ロジャー (ロ = 6, ジ = 4, ャ = 8), but why 55, when any number would do?? Because it's also for 五/五 or Nika Nika.
Drum of Liberation sfx Don-do-tto-tto ( ドンドットット" )