Set in a secure prison high in the White Clouds, the [Mysterious Prison] event follows a tense standoff between guards and intruders. Lavia and her brother Jordan, both C Rankers, work as prison enforcers. Their latest challenge: protecting a mysterious young prisoner—Dante’s little sister, a dangerous criminal with secrets of her own.

When the notorious mercenary group Fangs launches a violent breakout to free her, Dante himself arrives—not to join them, but to stop them. Torn between family and duty, he joins the guards in a desperate fight to keep the prison sealed and prevent chaos from spilling into the sky-bound world.