Riannon is a key character in the anime series 'Tears to Tiara'. She is a gentle and compassionate priestess with a strong sense of duty towards her people. Riannon is the sister of Arthur, the leader of the Gael tribe, and plays a vital role in the series as she becomes the bride of the demon lord Arawn. Her character is central to the plot, as she helps to bridge the gap between humans and the demon world, while also developing a deep bond with Arawn and the other characters.