For this achievement , when you come back to Cleyra because black mage invasion, you will meet resident and they will ask to guide them.You should save 3 different couple of resident by answer which direction to go
For the 1st couple of resident you meet : guide them to right direction and follow them. After you will see a family, send them to left direction and follow the family. The last resident to save are a mother and her 2 child. Answer them to go right direction on the bridge.
Follow them they will ask if it's safe now , you can answer yes.
Go to the temple , after some conversations , achievement will pop up after you see Beate.