Chapter 520 is titled "Gorgon's Eyes".
Luffy uses Gear Second, as the audience are surprised at the smoke coming out of Luffy. Sandersonia attempts to attack Luffy, but he is too fast for her to hit him. Luffy successfully hits Sandersonia and Marigold, which prompts Hancock to ask what they are playing at. Sandersonia and Marigold start attacking Luffy again with their strongest attacks, but he launches his "Jet Gatling" attack, and proceed on to tying their snake tails together. The sisters panic, helpless, and Sandersonia nearly falls off the arena and the clothes on her back are burned off. However, Luffy covers her back in order to hide her slave mark, much to her shock. Hancock, realizing the severe situation, orders the audience in the area to leave. Sandersonia questions Luffy on why would he help her, and Luffy shows his kindred heart, causing Hancock to cry.
As Luffy activates Gear Second, the audience is amazed by the steam coming out of his body, but believe that he could never defeat Sandersonia and Marigold. However, as Sandersonia uses her eight branches technique, Luffy dodges all of her attacks with relative ease, and she wonders at how he is able to dodge all of her moves despite her using Haki and realizes he is able to dodge them because he is too fast that she herself not able to keep up. Luffy, with his astonishing speed, wraps his arm around her neck and throws her to the ground, surprising everyone. Marigold proceeds on swinging her weapon at him but he dodges and prepares to strike her and she defends herself stating it won't work. Despite her claim, Luffy uses Jet Bazooka to destroy her weapon and send her flying back. The whole crowd is shocked that Luffy is winning the fight and Hancock becomes irritated at Luffy and asks her sisters what the two of them are doing. Her sisters apologize and say they'll end things now.
Sandersonia uses her eight branches technique again while Marigold uses a technique that lights her hair on fire while the crow marvels at them using their strongest techniques. Luffy bends backwards as the sisters prepare to finish him and Luffy unleashes a Jet Gatling on them, once again shocking the whole crowd that he easily defends himself from Sandersonia and Marigold's strongest attacks. He kicks them in their stomachs, sending them crashing at each other and Sandersonia's hair is lit on fire from Marigold's technique. Marigold apologizes and tries to push herself away only to see their tails tied together while Luffy is doing the victory sign. Sandersonia tries to put herself out and almost falls out of the ring and her clothes start to burn, causing Hancock to worry and notices her back is exposed. Luffy jumps on her and the crowd thinks he is trying to finish her off and he is just so cruel. As Sandersonia yells at him to get off, he tells her not to move and so no one will see her back causing the shocked sisters to realize that he is helping to protect their secret.
Hancock thinks back about her telling Luffy that what's on their back is something they would rather die than let others see it. She then orders everyone to leave the arena, at which they do, realizing that Luffy is in fact, helping Sandersonia and the arena becomes empty. Marigold is amazed that a man would actually help them and Sandersonia asks Luffy why would he help them as they are enemies. Luffy responses that the thing on their back has nothing to do with their match while Nyon comments on Luffy's kindness and how Hancock and her sisters have been saved by the man they just tried to kill. Hancock, after seeing Luffy's kind personality, starts to weep.
- Luffy defeats Sandersonia and Marigold.
- Sandersonia's clothes are burned off and almost exposes the "Gorgon's Eye", until Luffy jumps on her back and says that he will protect their secret.