Diana resides with her grandmother Towa in the forest of Arborville that Celebi protects. She is seemingly more easy-going than her grandmother, but does get defensive when the things and people she holds dear are threatened. Brock, of course, has the hots for her.
Diana met Ash and his friends when her grandmother was warning them about going into the nearby forest. Brock flirted with her and invited her into the forest with them for her to protect them, but she stayed behind. When the trio returned with an injured boy, they went to Diana first, but he woke up before she was able to do anything. After hearing Sam was with a Celebi the day he disappeared, Diana came to the conclusion that it must have been because Celebi felt they were both in danger and they had to get out of there as fast as possible.
After seeing a storm of earth, grass, and plants, Diana and her grandmother went to rescue Ash, Sam, and the others from the forest in a blimp. Soon after picking up Ash and the others, Celebi's Hyper Beam brought the blimp down. After Celebi was able to fight off the effects of the Dark Ball in which it was captured by the Iron-Masked Marauder, it remained injured and weak. Brock suggested putting it into the water, but because it was tainted, it had no effect. Diana then suggested that Suicune—who had fought against the Iron-Masked Marauder—could purify the water.
When the Marauder is defeated, Diana and her grandmother and the rest of the Forest Pokemon confront him before the Forest Pokemon use string shot tie up the Marauder.
Diana is last seen waving goodbye to Ash and his friends as they set off to continue their journey.
- Diana and Towa's hairstyles may resemble Kris's hairstyle, as all of them has bunches behind their ears. However, Diana and Towa have green hair (Towa has light-green hair as an elderly woman) and Kris has longer bunches than Towa or Diana.