"Project A-ko 4: Final" is the fourth installment in the "Project A-ko" series, continuing the adventures of the superhuman high school student A-ko Magami and her friends. The story is set in Graviton City, a futuristic metropolis where A-ko, her best friend C-ko Kotobuki, and their rival B-ko Daitokuji navigate a chaotic blend of school life, intergalactic conflicts, and personal rivalries. The narrative picks up with A-ko and B-ko reluctantly teaming up to protect C-ko from a new threat: an alien race seeking to exploit her mysterious powers for their own purposes. C-ko, unaware of her latent abilities, becomes the focal point of the conflict, forcing A-ko and B-ko to set aside their differences.

The plot unfolds as the alien forces, led by the enigmatic Commander Z, launch an invasion of Graviton City, deploying advanced technology and formidable warriors. A-ko, with her immense strength and combat skills, takes on the role of Earth's defender, while B-ko utilizes her family's vast resources and technological expertise to counter the alien threat. The dynamic between the three main characters remains central, with A-ko's determination, B-ko's cunning, and C-ko's obliviousness driving much of the humor and tension. The story balances action-packed sequences with comedic moments, maintaining the series' signature blend of over-the-top battles and lighthearted interactions.

As the conflict escalates, the narrative delves into the origins of C-ko's powers, revealing ties to an ancient alien civilization. This revelation adds a layer of intrigue to the story, as the characters grapple with the implications of C-ko's true nature. The final act culminates in a climactic battle where A-ko, B-ko, and their allies confront Commander Z and his forces in a desperate bid to save Graviton City and prevent the aliens from achieving their goals. The resolution ties up key plot threads while leaving room for the series' characteristic open-endedness, ensuring the story remains engaging and true to its roots.