In the year 2025, colossal beings known as galactic monsters descended upon Earth. To combat this threat, humanity established the Anti-Kaiju Defense Force E-RDE. Its most effective weapon was a shy young boy named Tetsuo Yabusame, hailed as humanitys savior, and his giant robot partner, Yukio, officially designated the Earth Defense Robot Snowman. Tetsuo, who had no friends other than Yukio, piloted the robot in a desperate final battle against the invading swarm. The battle ended in disaster. Yukio was destroyed, and Tetsuo narrowly escaped death by fleeing in an emergency pod, entering a state of cold sleep.

Eight years later, the pod finally returns to Earth. But when Tetsuo awakens, the world he once defended has vanished. The planet is a unrecognizable frozen wasteland, its surface buried under a perpetual blanket of ice and snow. This new, desolate world is now known as Snowball Earth. The fate of humanity is unknown, and the cause of the global freeze is a mystery.

Alone and carrying the weight of his last promise to Yukio, Tetsuo steps out into this alien, frozen landscape. He soon discovers that pockets of humanity have survived by adapting to the harsh new environment. One such refuge is Mishima Mall, a fortified community built within a vast shopping complex. There, he meets Ao Nogi, a curious and resourceful kaiju tamer who protects the mall by controlling a heat-collecting monster called the Land of Men, while also serving as the malls harried chief accountant. He also encounters Hagane Takimura, an enthusiastic and highly skilled engineer who can create close-combat anti-kaiju weapons and whose natural cheerfulness helps bridge the gap between the withdrawn Tetsuo and the rest of the world.

Tetsuo’s arrival, however, is not welcome by everyone. He is met with hostility by Isseki Sagami, the leader of a powerful group of kaiju tamers known as the Light of E-RDE (VIERDE). Sagami harbors an intense hatred for Tetsuo, the so-called Savior who disappeared when humanity needed him most. His followers include aggressive brawler Nayuta Izumi, calm sniper Tamiya Sakurai, and others who control their own powerful kaiju. As Tetsuo struggles with his own crippling shyness and the trauma of his past, he must navigate the politics of these survivor settlements. He is drawn into a conflict to uncover what happened to humanity, how the Earth froze over, and whether he can ever fulfill the promise he made to his only friend. The series follows Tetsuo as he journeys across this snowball Earth, forming new bonds and confronting a world that has both forgotten and resents its former hero.