In the year 2xxx, Earth was rapidly heading toward destruction. The cause was humanity. Extraterrestrials watching this gathered to protect and restore the planet's environment. Among them, Thalassa, a representative of the Physico race who owns and protects many planets and possesses time-manipulation powers, stepped forward. With absolute power, Thalassa rewound time for the planet Earth itself. However, unwilling to interfere with the lifespans of living beings, he erased all human memories, lowered their intelligence so they could no longer develop science and would live among animals, and sent them back to the Earth of year XX. It was a second chance. Earth became a massive laboratory where humans were brought in for monitoring, protection, and observation. Among the humans brought in as usual, one stood out: Guest. While a few aliens kept humans as pets, what Thalassa felt wasn't a mere protective instinct for a pet. He wanted to nurture, control, and train Guest never to defy him, while simultaneously showering them with love. This twisted desire was something he had never felt for his own kind. In fact, he had never even considered marriage... To investigate Guest further, Thalassa placed them in a human cage for protection and research purposes and headed to his spaceship.