One day, during the usual softball shenanigans, Nobita saves a stray dog from drowning. He named the dog Ichi and started taking care of him, as well as taking in and rescuing several animals both domestic and wild. When it proves to be too much to take care, Nobita uses Doraemon's spare pocket and time machine to send the animals 300 million years in the past and utilizes the Evolution Ray to evolve them. When the gang pays a visit to Ichi and the others' home later, the time tunnel goes haywire and ends up sending them 1000 years after their original time destination where they discover a city populated by sentient animals.
