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Rhyanna is a character of the day who appeared in Try for the Family Stone!. She is the older sister of Mitchell.

Rhyanna asked Ash and his friends to help find her brother after he ran away with his newly caught Murkrow. He was angry with her after she kept defeating him in battle over and over again. Her grandfather told her about the Dusk Stone; thus, she wanted to find it so that she could evolve her Misdreavus into Mismagius, which could use incantations to make Mitchell happy.

With Brock's help, she found the Dusk Stone. Unfortunately, Team Rocket intervened, captured her Misdreavus, and tried to steal the Dusk Stone as well. However, she would not let go of it and put herself in danger. She was eventually saved by Mitchell's Murkrow, who arrived just in time to help. Seeing that Mitchell was feeling much better, Rhyanna realized that she would no longer need to evolve Misdreavus. She and her brother decided to battle for the Dusk Stone, awarding it to the winner of the best of ten battles.

(Source: Bulbapedia)