He is a prominent fighter in the Heavens Arena and an apparent celebrity. Lives on the 200th floor as a fighter, uses martial arts and is very skillful in hand-to-hand combat. He had accumulated enough wins to become a Floor Master.
Two years ago, Kastro was defeated by Hisoka in the Heavens Arena making it his only loss. After this, he trains rigorously to improve his Nen and gains nine wins and then challenges Hisoka for his tenth.
He challenges Hisoka to a rematch. Although he was born an Enhancer, Kastro's "Doppelganger" ability completely ignored his strength and used Conjuration and Manipulation abilities. An Enhancer's maximum ability in these fields is 60% at best, so for Kastro is difficult to use and requires a lot of nen and concentration.
Despite this Kastro combines his two abilities to cover the defects of his double, making a letal combination, but Hisoka takes advantage of Kastro's weaknesses, distracts him with his abilities and ultimately kills him.