In this guide, you will find how to adopt the Calisson Chicken in Fire Emblem Engage.
In one of the very first maps, you will find this chicken. You can explore the area once you complete a map, and you may find this chicken. Make your way back to the home base, go to the donation board in the cafe and then upgrade the Firene donation to level two. It will give you the Callison chicken requirement to get it.
Now you either have to wait until the future town that stocks the Calisson chicken or if you play a bit longer, you will get skirmish missions and other missions that appear at towns you’ve already visited. It will allow you to go back to complete the mission, then explore the area, and you will get the chicken.