What item does Ditto find in Pokémon Pokopia that belonged to its trainer?

Ditto finds an old Pokédex that belonged to its trainer in Pokémon Pokopia.

The discovery is important because Ditto uses the trainer's appearance as the basis for its human form. The Pokédex therefore connects the player character's present adventure with its personal history and with the humans who once lived alongside Pokémon.

A Pokédex is an electronic encyclopedia used throughout the Pokémon franchise to record information about species. In Pokopia, this familiar object has a story function beyond cataloguing Pokémon: it is one of the clues linking Ditto to the absent human world.

The item is easy to confuse with a Poké Ball because both are iconic Pokémon-world objects. However, the Pokédex is the relevant discovery in Pokopia's opening story, while the game’s central progression focuses on rebuilding habitats and assisting Pokémon rather than catching them through a conventional battle system.