Oh lawd.....
You comparing Nika to the Berserk verse just gave me flashbacks to a time I came across a One Piece x Berserk crossover comic parodying the Eclipse from Berserk.
The roles are:
Luffy = Griffith.
Zoro = Guts.
Nami = Casca.
When Luffy goes full Griffith after discovering nothing on Raftel and finding the Behilit, he turns into a constantly grinning, near always giggling little shit as he is corrupted into demonhood.
My brother in manga, that comic forewarned the coming of the abominable Nika.