Each Tactician can carry one Animal Companion. 

Animal Companions have a Talisman type. 

and when equipped on a Tactician of the same type, they amplify the effect of the Tactician's Talisman.

Animal Companions unlock at Fortress Lv.10,

and you can purchase them at the Animal Market, which you can visit by tapping the Animal Companion next to your captain character.

※ If you have an [Animal Companion Invitation], it will be prioritized for use.