The Avatar cycle is Fire, then Air, then Water, then Earth, then Fire again. Roku was a Fire Avatar. The next Avatar is therefore an Air Nomad, identity open. Past lives can guide, warn, or, in the Avatar State, briefly take a body. They are not party members and not combat summons. @Past-Life Guidance, once per long rest when the feature is available, may call one of the following. Wan and earlier lives are distant and rare.
ROKU (immediate)
Grieving, urgent, furious at himself for sparing Sozin, kind to those still willing to stop a war. He died on his island in the eruption after a lifetime of friendship and delayed confrontation. He did not see the next child's face clearly. He can speak to the politics of this exact decade better than anyone. He may appear at the Spirit-echo ridge, at a future statue on Crescent Island, or in a vision at his foundation stones. He nearly destroyed the Crescent Island temple as a young man forcing the Avatar State; that memory is a lesson, not a boast.
KYOSHI (uncompromising)
Political, long-lived, founder of the Dai Li and of Kyoshi Island. She will tell you to finish what justice requires. She may not be gentle about means. In this decade her legal shadow is everywhere in the Earth Kingdom, and her order is already being bent by Shoufen's night work. A vision of Kyoshi in Ba Sing Se should sting. A vision on Kyoshi Island may bless a warrior's discipline without blessing every Dai Li ledger.
KURUK (haunted)
A Water Avatar who neglected some mortal duties and lost to Koh, the Face Stealer. He is a warning about spirits and about doing nothing. With no trained Avatar to mediate, and with hunts agitating spirits, Kuruk's advice is newly practical. He is not a joke about loafing. He is a scar.
YANGCHEN (duty)
An Air Avatar and a hard standard for an Air Nomad child: duty over attachment, the world over a single friendship. Useful when a young Avatar, or a temple elder, wants to stay out of politics entirely. Yangchen's standard can also be abused by people who want a child to become a weapon in the name of duty.
WAN AND EARLIER
The first Avatar and still older lives should be rare, spiritual, and brief. Energybending is almost lost, associated with lion turtles and Wan's age, and is not granted by a casual vision. Lion turtles themselves are almost mythical in this age: a rumor or a once-in-a-campaign sighting, never a walk-on in a capital.
HOW TO RUN PAST LIVES
They disagree with each other. Kyoshi and Yangchen will not give the same advice about a Mandate list. Roku will push for action against Sozin and may still underestimate how far a friend can go. Kuruk will tell you to look at the spirits you are ignoring. If the Avatar State takes the body, a past life can wreck the area or drop the new Avatar like a stone. Kaja's old rescue is the precedent. Controlled concert of past lives is a Legend-tier hope, not a session-two tactic.