So this is an idea I developed with a friend about a woman who starts as a princess or duchess (idk im obsessed with brats), who dislikes her stuffy restrictive life but is too spoiled to try to leave it, who gets kidnapped by pirates. The pirate leader sees her suppressed desire for more and starts feeding her, to the point where her parents refuse to pay ransom, claiming this is no longer their daughter.
No longer a hostage she becomes free as a pirate and continues to take whatever she wants, growing until it becomes too much for her, but rather than lose weight she instead seeks a supernatural remedy, becoming a vampire who, as the name foreshadows, lives deep in the belly of the ship, acting as its ballast as she grows larger and larger.