Pulled out of the ocean onto some floating debris of the destroyed Blue Fleet base, Hayami once again encounters the amphibious woman who now offers him food and companionship. But it doesn't take long for her sisters and other assembled Zorndyke creatures to track them down. The marine amalgams, though, don't attack but rather surround the star-crossed duo in anxious anticipation.

Still submerged and trying to piece together any semblance of a strike unit, Blue 6 and crew seek out a mammoth nuclear torpedo in the hopes that its strength will be enough to stop Zorndyke in Antarctica.

Surface side, a musuca approaches Hayami, now stripped of everything he cares about, with the offer to take him back to Blue 6. Taken aback not only by the musuca's ability to speak but also by its kinship with the amphibious woman, whom the titan creature calls Mutio, Hayami renews his sense of diplomacy and is determined to confront Zorndyke personally for answers to the old man's motives. However, Hayami first has to pacify a Blue Fleet that's out for blood.

Hayami's pacifism now butts heads with Commander Iga of Blue Submarine No. 6, currently under orders to proceed to Antarctica to nuke Zorndyke. The glimmers of hope don't shine from the military might of the Blue Fleet nor the villainous sludge on the Phantom Ship. Hayami alone realizes that the cycle of war imbedded in the emotions and philosophies of all creatures on Earth will play out until life itself is eradicated forever.

Hayami's arc moves from utter apathy about the fate of the world to a passionate need to save humanity. And in this journey he exorcises laden guilt from his past primarily from his relationship with Katsuma, a friend and fellow submariner who years ago dragged him along on an initial secret meeting with Zorndyke. In 'Pilots' Hayami learned that Katsuma didn't die in the botched operation but, instead, was partially transformed by Zorndyke into an aquatic mutant. And the transmogrified Katsuma is currently helping the Blue Fleet get to the Antarctic base, being the only one who has ever returned from it. This opens up the floodgates, so to speak, of Hayami's memories.

As he sinks to the bottom of the ocean in the episode's opening sequence, glimpses of his relationship with Katsuma flash before his eyes. He confesses that he has a fear of water instigated by a boyhood accident in which he was cast into the sea without being able to swim and had to be rescued. Katsuma also saves him from the sea when they both failed to reach Zorndyke the first time. And now the amphibious woman, who finally has a name, Mutio, saves Hayami from the sea. Despite his talents in the deep, Hayami belongs on land. This becomes the central issue when Hayami encounters the musuca who recognizes the commonality of all the beings on Earth and the propensity they have to murder each other.

Therefore the great musuca becomes more akin to Hayami than any of the humans. Like Hayami, this musuca hasn't followed the chain of command blindly. It questions the violence ingrained on each side, questions the eradication of an entire species, and questions the intentions of the mysterious Zorndyke whose actions actually infer a higher purpose. The musuca asks, "Why did papa grant us sentience?" Hayami iterates in less direct introspection, "All I do is get rescued from the sea." But in this line he questions why he has been granted talents in the sea if all he does is get saved from it. Both the musuca and Hayami begin to hear a call to Zorndyke's higher purpose. And both are ready to sacrifice themselves for this purpose despite not knowing what it is.

However, the Phantom Ship and Blue 6 have each exhumed dormant nuclear weapons to use as a last resort against the other, polarizing the narrative between the pacifists and the war mongers rather than the good guys and the bad guys. In "Hearts," director Mahiro Maeda draws even clearer similarities between the Blue 6 and Phantom Ship crews. One of the sailors validates Kino's waning convictions against Zorndyke by declaring that the Blue Fleet is fighting to avenge the deaths of ten billion people and to keep humanity alive. One species life, then, is worth another's death. The exact same sentiment slithers through Verg's villainous teeth when he says, "They saved the life of a human, the enemy we are sworn to destroy." And this statement echoes the bloodlust from the first episode when Hayami saves Mutio to the chagrin of an armed Kino ready to blow her away.

"Hearts" continues to march defiantly away from promoting self-righteous patriotism, re-examining culturally entrenched perceptions of right and wrong.