Everstone

The  is an item in Magikarp Jump.

In the main Pokémon games, Pokémon holding an Everstone would not evolve.

The Everstone can be broken by tapping Magikarp repeatedly. This allows the Magikarp to evolve once it levels past level 20, triggering the Random Encounter Adios, Gyarados!. Once the Everstone has been broken, the Trainer will receive another Everstone.

The Everstone can only be broken once.