One Piece Chapter 35, page 4-7: THE STEEP SLOPE AGAIN

Usopp and Kaya scream at the kids to stop. Jango and Zoro look on, bewildered by the children's reckless actions. The kids finally stop, deciding to show Kuro "mercy," and turn to Usopp, demanding to know why he didn't tell them he was fighting. They argue over whether his secrecy was "disloyal" or "dishonest.

Usopp desperately orders the kids to run away, but they stubbornly refuse, wanting to stand and fight alongside their captain. Suddenly, Kuro stands up behind them, his long clawed gloves crackling menacingly. The kids freeze in absolute terror as they realize the monster is back on his feet.

Kuro walks right past the terrified kids without attacking them, leaving them confused. He stumbles slightly, adjusting his glasses with his palm. Luffy watches from a distance, commenting that Kuro's movement was quite an odd attack and expressing curiosity about his abilities.

Kuro deduces that Luffy possesses a Devil Fruit power. Luffy cheerfully confirms, "YUP! I ATE A 'GOMU GOMU FRUIT'!! AND I'VE BECOME A RUBBERMAN!!" The Black Cat Pirates are shocked to learn that Devil Fruits actually exist, and Jango realizes Luffy's stretching arm wasn't an illusion.