Rika Manabe begins as the initial protagonist who transforms into Saint Djibril. Her deep bond with Naoto Jinno evolves from childhood friendship into adolescent romance. Their summer confession intertwines with supernatural events when the demon Asmodeus attacks. Recruited by the angel Luvriel for the celestial war, Rika becomes Saint Djibril by wearing Luvriel's halo. Her power relies on accumulating Amore energy through intimacy with Naoto.

As Saint Djibril, she battles demonic forces using Amore-fueled abilities, manifesting light-based attacks and angelic wings. Her primary adversaries are Asmodeus and the corrupted Misty Mei, formerly her classmate Meimi Otonashi. Maintaining her combat effectiveness requires her continued connection with Naoto for Amore generation.

Later captured by the demon Rococo, Rika undergoes forced transformation via tentacle creatures. This corruption turns her into Dark Djibril, marked by bat-like wings, red eyes, and control over Rococo's tentacle monsters. Her personality alters, finding twisted pleasure in the torment she once endured. As Dark Djibril, she opposes the new protagonist, Hikari Jinno (Djibril Aries), recruited to rescue her.

Rescued and purified, Rika returns in subsequent stories. Her role shifts to supporting newer Devil Angels like Nagi (the New Angelic Gaia Interface) against technological threats. She also participates in dimensional conflicts when transported to warring-states era Japan, maintaining her link to Naoto throughout. Rika demonstrates resilience through repeated confrontations with recurring antagonists like Misty Mei across multiple arcs.