Diana, a Jupiter Sister and divine rebel against Old Hell's destruction, survives by sharing consciousness within host Tenri Ayukawa while retaining her own identity. She communicates through reflective surfaces like mirrors to guide and influence Tenri's actions. As catalyst for the Goddess Arc, Diana tasks Keima Katsuragi with locating and awakening her five siblings—goddesses inhabiting Keima's past conquests who retain fragmented memories. She imposes a critical mission deadline due to Vintage's threat; the organization seeks to eliminate the goddesses to resurrect Old Hell. Lyrics reflecting her supportive role include "Whenever you need me, I’ll come out right away" and "Take your time and tell me what is on your mind."

Diana demonstrates protective loyalty, especially toward Keima. After Vintage’s assault renders Kanon Nakagawa comatose and leaves Apollo dormant, she intervenes during Keima’s depression, compelling him to persist. She later coordinates awakened goddesses to merge powers, purging Vintage’s curse from Kanon—showcasing her leadership among the Jupiter Sisters.

The goddess shapes Tenri’s growth toward assertiveness and emotional openness, while Tenri’s experiences deepen Diana’s grasp of human bonds. Their synchronization peaks when Tenri manifests temporary wings following Keima’s apology, symbolizing their evolving connection. Diana’s lyrics incorporate "natural laws," linguistically linking to Tenri’s name.

Throughout the arc, Diana prioritizes her sisters’ survival and halting Old Hell’s revival. Her existence within Tenri forges a dual-layered dynamic where both entities evolve through shared experiences and external threats.