Towa is Diana's grandmother from Celebi: Voice of the Forest.
Biography
40 years in the past, a young Towa gave Sammy a warning about encountering The Voice of the Forest. Before the young man entered, Towa gave him a loaf that she made fresh. She later sensed a strange occurrence from the forest, wondering if time traveling was at work.
In the present, Towa warns Ash and his friends the same warning she gave Sam years ago. She was overwhelmed when she saw the missing young man for the first time in decades. Towa later returned the sketch book that the boy dropped before he disappeared. Hearing Sam speak of Celebi, Towa revealed that the Pokémon he encountered that day was the Voice of the Forest, the spiritual guardian of the forest.
Etemology
Her name Towa (トワ) means eternity, which may refer to Celebi's time travel abilities.