Can you and your magic sword save the kingdom from death herself? Infiltrate a tower full of skeletons, decipher its secrets, and escape with your team!

Undying Fortress is an interactive dark epic fantasy novel by Yeonsoo Julian Kim, author of The Fog Knows Your Name, where your choices control the story. It’s entirely text-based, 500,000 words and hundreds of choices, without graphics or sound effects, and fueled by the vast, unstoppable power of your imagination. I sat down with the author to talk about their latest game and how their writing has shifted between their first and second Choice of Games titles.

Undying Fortress releases December 19th; you can wishlist the game on Steam today!

You’re one of the most prolific game designers/writers we’ve ever worked with at Choice of Games. You’ve written for TTRPGs and LARPs and more besides. What else have you been up to since The Fog Knows Your Name came out?

I think the two projects to come out since Fog that are closest to my heart are Women Are Werewolves, a card-driven storytelling game I co-designed with C.A.S. Taylor, and Home which is a map-drawing horror game I co-designed with Doug Levandowski. Clearly my love for all things supernatural is still going strong! I also wrote for the Avatar Legends RPG and was a designer for the Chucky boardgame which were both fun projects to work on.

On a less fun note, I’ve actually spent a big chunk of the last few years trying to recover from long COVID which slowed me down a ton, to say the least. I’m especially thrilled to see Undying Fortress sent out into the world because for a long while there I wasn’t sure if I’d ever bounce back enough to make it happen. It’s been quite the journey! I owe a big thank you to my long covid support group and my friends and family who helped to get me to this point—and, of course, my editor Rebecca.

Undying Fortress is a serious departure from the supernatural kind of YA feel of The Fog Knows Your Name, which I also think is one of our best all-time game titles. Tell me about this pivot in ChoiceScript storytelling.

It means a lot to me that you like it! I have so much fondness for Fog and my experience writing it. I sometimes listen to the music I would have on repeat back while writing it so I can sit in that atmosphere again.

I think the pivot mainly came from a desire to explore different genres as a writer. I read very widely across genres so I often think about what stories I’d want to tell in those different spheres. Of course, the horror element is a strong presence in both The Fog Knows Your Name and Undying Fortress, and I think horror is probably my home, so to speak.

This is a real epic fantasy of a game. Where did you draw inspiration for Undying Fortress and the kingdom of Serendal?

I remember when I was putting the pitch together for Undying Fortress and then the outline, I kept thinking about how it felt so different from most of my writing as an adult but so inspired by the stories I would write growing up. I consumed so much fantasy media as a child and teenager and I think I pulled a lot of inspiration from what I loved back then – books like The Lord of the Rings, anime like Slayers, games like Fire Emblem and Neverwinter Nights.

I’ve also always been drawn to stories involving the undead and necromancy. The Korean series Kingdom was a huge influence on Undying Fortress. When it came to creating Serendal and the people and cultural influences within it, I started by taking inspiration from my own ancestry. Serendal is, in many ways, a fantasy version of Joseon era Korea if there had been a huge influx of Welsh citizens several eras prior (players who are interested in learning more about this might have fun favoring History and Theory as a stat during their playthroughs). I also envisioned Serendal as a kingdom with very robust trade routes that connect it to different empires and territories throughout the equivalent of the Middle East, so there’s a long history of cultural exchange and migration tied to those routes.

What will our readers find most surprising about this game?

There are a lot of twists and turns regarding the primary antagonist of the game, an entity known as the Carrion Mother, and her history in Serendal. My hope is that readers will feel like adventuring scholars, uncovering secrets about the world and its past as well as the history and nature of mortuary magic. I kind of like to think of the game as an academic dungeon crawl, because while some characters are there purely to contain any potential threats inside the fortress, others are there to study every secret it has to offer.

Did you have a favorite NPC in the writing this time?

It’s probably got to be Hani. I apparently love writing characters who are very tormented by their own emotions. I don’t want to spoil too much about Hani’s backstory, but they have some very intense and unpleasant emotions that developed due to some highly unusual circumstances. I’m sure some players will really feel for Hani while others will want to chuck them off the top of the fortress.

Eredith was also really fun to write because she’s so powerful and competent and just filled with knowledge. Yet she still has made decisions that haunt her throughout the course of the story.

What will you be doing next?

I’m currently working on a botany-themed tabletop roleplaying game called Bloomfall. Sharang Biswas and I are working with the National Academy of Sciences’ LabX to create the game. I’m also in the beginning stages of putting together my Substack where I’ll largely be writing about game design, narrative, and my creative process. I have a dungeon synth tabletop roleplaying game I’ve been very slowly working on over the past couple of years and I’m hoping to have that ready for playtesting in 2026!