Kujira no Kora wa Sajou ni Utau

A character named Chakuro serves as an archivist on a structure referred to as the Mud Whale, where he documents the life and death of its inhabitants. As a member of a group with a short lifespan and the ability to use thymia, he is aware of his limited time and aims to create a more comprehensive record than those before him. The tranquil and isolated life aboard the Mud Whale is disrupted when a scouting team encounters a young girl who appears to have knowledge about their home that exceeds their own.