Mana, Karina, Naoto, and Yuuki are childhood friends and ordinary high school students. They believed that their ordinary days would continue on in life, until one day Karina brought home a four-legged "pet human"... The new family member they were introduced to was an 8-year-old boy with restraints on his hands and feet and a collar. He looked just like them, but somehow animalistic and completely different... This is a world where humans are allowed to keep "pet humans". However, the next day, they received the shocking news that Yuuki was a "pet human"!