Robin receives more focus in the final battle against Black Maria than she has in years. And honestly, it feels like it just stopped working again. We get more of a callback towards Sanji asking for Robin’s help, and we see why what Sanji did meant so much to her.
Sanji asked for her help. The girl who was a demon, whom everyone shunned, and whom no one trusted, had people who needed her. This is what allowed her to become a monster to them.
Robin creates an enormous demonic representation of herself and defeats Black Maria.
He is similar to Chopper, who assured that he would be a monster to his friends, those who would always be by his side, regardless of whether he was a monster or not.
Oda took full advantage of the crew dynamics in this fight against Black Maria to be satisfactory. It’s the same formula as Kalifa’s fight, but, thematically, it works a lot more than that, as Kalifa’s fight was about presenting Sanji’s weaknesses towards fighting women while only playing an element of the Black Maria scenario. It was more about reinforcing the dependence and trust the Straw Hats had for each other, especially if they were in a situation they couldn’t handle on their own.
As far as the Fishman Karate technique and the new giant demonic form, let’s not forget how Robin’s character is portrayed in Chapter 1021.
Prior to this fight against Black Maria, Robin had confidence in the Straw Hats and Luffy, but it was unclear if she had confidence, which is a vital piece of power in One Piece.
Self-conscious about not being as strong as some of the other hitters, Robin recognized her in flashback. Her friends in the Revolutionary Army were concerned for her safety, saying that she might not be able to take care of herself after returning to the Straw Hat crew.
Now she jumped headlong into a fight she didn’t know the outcome of, testing a new ability in the heat of battle. She fought with confidence and overcame a major hurdle. This is some of the greatest Robin development we’ve had in years.