Don is the younger brother of Ran, both originating from the Otsuno tribe. After Tyranno destroys their tribe, Don is separated from Ran. He reunites with her during Ryu's journey and subsequently joins Ryu and Ran as a permanent member of their traveling group.

As the group's child character, Don relies primarily on Ryu and Ran for protection across the prehistoric landscape. Recognizing the dangers of their quest and contemplating parting ways to safeguard the siblings, Ryu actively trains Don in archery to bolster his ability to defend himself and his sister.

Don fights alongside the group against threats including Tyranno and hostile human tribes. During one confrontation, Gan of the Kasta tribe sacrifices his life to shield Don from a spear thrown by Karim, a follower of Taka.

Don remains part of the core group throughout the journey. After Ryu reunites with his birth mother, Esta, Don continues traveling alongside Ryu, Ran, and Esta into future adventures.