One form of philosophy that’s been especially historically important in East Asian cultures including Korea, and which in fact remains important in terms of its influence on culture, is feng shui, or as it’s called in Korean, pungsu.
Although The Pirates is clearly designed as a Korean-flavored knock-off of the then-popular Pirates of the Caribbean film franchise, for what it is, it’s actually pretty good. I mean, don’t go in expecting historical veracity or brilliant dramatic performances, but if you’re looking for inspiration for a nautical campaign set around the coasts of Jeosung (or a nautical leg of a larger campaign in the setting), it’s very much worth checking out.
The character Byeon Gang-soe is often summarized as a kind of “Korean Casanova” because both figures are famous for the same thing—the “legendary libido” alluded to in the title of this film—but beyond that one trait, the two have very little in common: while Casanova was a priest, a man of letters, a spy, and a con man, Byeon was a worthless good-for-nothing bum.
The Along with the Gods duology is an adaptation of a popular webcomic by the same title. “Webtoons” are extremely popular in South Korea, and many of them include fantastical elements. While some of these webtoons really just rehash Western fantasy and science fiction tropes, others explore fantastical concepts, religious ideas, magic, and fantasy narratives of a more distinctly Northeast Asian kind. Attentive GMs will also find a wealth of compelling detail to weave into their games. Magical (or even mundane) shields, scrolls, or grimoires could easily be illustrated with a scene from the underworld.
Jeon Woochi is a figure that shows up in several Korean folktales and older texts. He’s kind of the Korean equivalent to Merlin or Gandalf or Elminster, except that unlike these other figures, he’s also a thief, a trickster, a loudmouth, and prone to getting himself into trouble and then out of it by the skin of his teeth, and by dint of his magical gifts. Which is to say, Jeon is a lot more fun than Merlin or Gandalf or Elminster, and a great, interesting model for a Wizard PC or NPC in Jeosung.