In a serene park, a lone figure faces an abrupt demonic assault that seeks to draw out a latent power from deep within. Back home, a stepsister's return from overseas leads her to join the same school as her brother, sparking quiet tension with his devoted partner. Their tender reunion is interrupted when a mysterious entity abducts the young woman, prompting an angelic visitor to explain the urgent need for a new bond with the stepsister to awaken a protector capable of restoring what was lost.