So as per the anime illustration the devil fruits unites with the user after eating and when that power which has been turn into a fruit synchronises in full with the mind and body of a man, it awakens and turns the user into that power itself. So a Zoan devil fruit awakening turns the user into the Zoan. Lucci became more leopard like, enhanced speed, strength and duration.
So Luffy is turning into Nika, his mannerisms are affected by Nika. So this is just the start. Luffy has to unite with Nika in full to further his horizons. He has been limited to rubber by the subconscious input of Shanks so once he finds out the truth of his fruit, its going to turn him into THE SUN GOD NIKA totally.