The whole "save the world by dating" premise finally stops being cute and becomes the thing it was always building toward: a kid watching every person he loves become a weapon in someone else's war. Isaac doesn't care about sealing Spirits or philosophical debates about humanity. He wants to kill Shidou and take everything that makes him matter. Shidou has no army, no secret power, no way out except the one thing he's always had: he refuses to let these girls fight alone. The relationships that seemed like fanservice are the only armor left, and they're not enough.

Shidou Itsuka has already sealed ten Spirits, and his ties to Ratatoskr now put him in more danger than ever. Isaac Westcott, head of Deus Ex Machina Industries, resolves to kill Shidou and seize the Spirits' powers, and he opens a full war on Ratatoskr. The organization must spend everything it has to keep Shidou alive while badly outnumbered. Their one hope lies with Kurumi Tokisaki, the Spirit of Time: Shidou has to seal her power so he can go back into the past and face the Spirit of Origin, the source of it all. This fifth season blends action, fantasy, mecha, sci-fi and romance.