The episode begins with Zero Two and Hiro reflecting on their experiences and relationships. Zero Two is struggling to come to terms with her past and her connection to the Franxx. Meanwhile, Hiro is trying to find a way to save the children and the Franxx from their fate.
You're referring to the anime series "Darling in the Franxx"!
The episode then shifts to a flashback sequence showcasing Hiro and Zero Two's time together in the past, highlighting their bond and relationship.
The show ends on a "paean to child-rearing," where the ability to create life and raise a new generation is framed as the ultimate victory over the stagnant, immortal VIRM.