Nergal apologizes to Serena and Artemis-Zygarde of her previous actions, and wishes to reconcile. To make up for it, Nergal manipulates the reality around them to show them her finest work: Ragnarök, the apocalypse that destroyed her homeworld.
Heidi and an Arceus go back in time to save them. The Arceus fights and defeats Friede, forcing her to flee from the midst of her assault. At the same time, Heidi collected some of Melony's shards and flies off to save others who are caught in the crossfire. In doing so, Heidi eventually caught up in a fight against a past version of Nergal. Fending her off, Heidi saves Jörmungandr and 50% of Leifi from the past version of Nergal. Upon collecting the cores and cells that were destroyed by the past version of Nergal, the present version of Nergal, Serena, and Artemis appear and inform her that they're all safe. Heidi gives the shards and cores to Nergal and flies off to find the Arceus from before.
Nergal, Serena, and Artemis return to the present and Artemis absorbs the cells and cores so they may recover. Artemis donates some of her active cells and one active core in order for Leifi to be completed once more.
Nergal gives Melony the Griseous Shards that Heidi had collected, giving her the final pieces that she needs to complete her core.
Heidi and the Arceus return to the present and Heidi returned home