Les Yay: Between Sono and Yura. The anime actually tones it down.
Supporting Protagonist: Arguably, Yura is this to Sonora's Hero role. While most of the plot does revolve around Yura's character arc, she often isolates herself and does a Face–Heel Turn that eventually leads to her essentially disappearing. Meanwhile, C³ stays relevant, and we see them worrying about Yura more than we see how Yura is feeling. Sonora is also the character to have a Dead Mentor and The Rival, normally reserved for the main character, and the show ends when she is about to leave to study overseas. In many ways, the show is written like a sequel to a series where Sonora was the main character and now she's in the process of Passing the Torch to Yura.