Diane was the princess of Dunyèdar, only second in line to the throne after Lumina, however, she was isolated from everyone’s sight and this had always been the case after an assassination attempt against her had happened, and out of protectiveness, Lumina ensured that Diane was locked away, out of complete sight to prevent any other assasssination from happening to her younger sister.

This negatively impacted Diane, who became shy whenever she interacted with her own sister or anyone else.