Chirithy

Chirithy are small, adorable plushy cat spirits. Each Keyblade wielder was assigned a Chirithy. Chirithy provides advice and guidance, along with presenting their wielder with trials with which to gather Lux, help others, and grow stronger. Chirithy are intrinsically linked to their keyblade wielders; if their wielder should die, then so will Chirithy, and if their wielder falls into darkness, then their Chirithy will become a Nightmare.
At one point during the period before the keyblade war, Chirithy presented their wielders with a Power Bangle, which allowed them to collect Lux more efficiently in order to power up their keyblades. However, the power bangles stopped working after the Keyblade War. Keyblades owned by the player characters in the game will be depowered to their base forms, and will need to be powered up again.
Chirithy may or may not have followed their wielders; it's possible for Chirithy to be destroyed without affecting the keyblade wielder.