Kaya inherited substantial wealth after her parents passed away, but she's dealt with chronic illness for years. Her caretaker Klahadore—a man her father had taken in off the streets three years prior—became her primary companion during this period. What she didn't know was that Klahadore was actually Captain Kuro in disguise, methodically earning her trust over those three years to eventually kill her and steal her fortune.
The one bright spot in her isolated, sickly existence came from Usopp, the village's notorious liar, who'd sneak up to her window and spin outrageous stories that made her laugh. Klahadore saw this as a threat and drove Usopp away, convincing Kaya that he was a bad influence. When Usopp overheard Kuro's conversation with the hypnotist Jango and rushed to warn her, she didn't believe him—and honestly, given his reputation, that's understandable. It took actually witnessing Kuro's betrayal for her to accept the truth.
After the Straw Hat crew defeated Kuro, Kaya showed her gratitude by giving them the Going Merry, which became their ship.
Years later, she spotted a bounty poster for "Sogeking" and immediately recognized it as Usopp—his nose gave it away. By then she'd decided to pursue medicine seriously, partly because she wanted to be ready to help patch Usopp up when he eventually returned from his pirate adventures. The former members of the Usopp Pirates made it clear they'd beat him senseless if he ever made her cry, which says something about how much she mattered to that group.
Content compiled by AnimeList.moe from publicly available sources.
