The I-401 returns to Yokosuka to pick up the secret weapon developed by the Japanese Government, the "Vibration Warhead", before returning to their base at Iwo Jima to make the final preparations for its journey across the Pacific. Meanwhile, Haruna awakens and meets Makie Osakabe, the child who rescued her. Pretending to be a human, Haruna keeps Makie company while Kirishima's core uses some of her nanomachines to make a spare body for her out of a Teddy bear. Takao arrives at Iwo Jima ahead of I-401 but is stopped by a vicious attack from unknown origin. Realizing that Makie is related to the deceased T?j?r? Osakabe, the creator of the Vibration Warhead, Haruna and Kirishima contact their flagship Kongou and are instructed to investigate further. In the occasion, the two mental models are introduced to T?j?r?, who is revealed to be alive, but bedridden. T?j?r? reveals that after several failed attempts to develop a weapon to counter the Fleet of Fog, he came with a plan to create an artificial being with superior intellect capable to succeed where he did not, and the only surviving offspring of said project is Makie, who was the true creator of the Vibration Warhead. To protect Makie from the government, T?j?r? forged his death and kept watching over her from the shadows but knowing he has not much time left and seeing how attached she became to them, he asks Haruna and Kirishima to take care of her. However, the army is already aware that Makie had made contact with ships of the Fog, and sends a unit to dispose of her.