This guide will help you to find the ancestor costumes for seven characters.
Getting 100% Costumes of All Characters
Enkidu (Plant Guy)
Go to the wolf clan. Talk to Enkidu. He shouldn't be very hard to find. When you go to camp, you should see him. Talk to him again. It will show a flicker of what his ancestors looked like. When you complete the "round" of the game. It will give it to you.
Go to Duskfolk and talk to her. She will meet you at camp the next day. Talk to her at camp and you're good.
Dumuzi (Blades Man)
Go to high town or Uruk. He will be in the building with the moon goddess sign. You know the drill. Talk to him, go to camp, talk to him.
Enheduanna (Skull Lady)
Go to Celestin. Isn't that nice. Swamps are so lovely, with mosquitoes! Anyway, find Enheduanna or Heduanna (her name is Long). Talk to her, go to camp, talk to her again.
His is hard to get. You have to find the moon temple. Do what Icarus told you (New, Full, cresent). Then fight the King. When the moon goddess shows up, forgive your brother. Forgive.
Ninlil (Ice Skater)
Her's is easy. Play a "round" as her. Then you get it.
Roa is very easy too. Play as her and then get the costume. Done.