Castle Swimmer is a fantasy LGBTQ romance webcomic by Wendy Lian Martin. It has been published digitally on Webtoon since 2019, and in print since 2024 by Ten Speed Graphic.
Plot
In a world inhabited by various species of mermaids, the prince of the sharks, Siren, learns of a prophecy to save his cursed people. The prophecy requires him to kill an individual known as the Beacon, who turns out to be a boy named Kappa. With Siren unwilling to kill Kappa, the two attempt to find a way to avoid their fates.
Development
Martin has cited the Little Mermaid world from the video game Kingdom Hearts as an inspiration for the work. She has also discussed a desire for explicit LGBTQ representation.
Publication
Digital
The comic started publication on Webtoon in 2019, updating on Sundays. The series has been divided into four seasons.
Print
In 2024, it was announced that Ten Speed Graphic would be adapting the series for print, with the first volume being published in October of that year.
Reviewing the first print volume, CBR praised the humor and underwater theming, but criticized the overuse of blue in comic's color scheme, stating it made certain scenes blend together. School Library Journal also reviewed the first volume. Ollie Kaplan of The Mary Sue labeled it as one of the best middle-grade and YA graphic novels of 2024.
By November 2024, the series had approximately three million subscribers. By June 2025, it had 344 million views.