A spin-off of Kaijuu Booska, a famous children's sitcom, taking place 70 years after the original story and features Tonda Daisaku's granchild, Koosaku, as the main character.

In the past, Booska and Chamegon set off into the cosmos to find new energy for the earth. They said they would come back in 20 years, but they've never returned… Then, after many years have passed and people have forgotten about Booska and Chamegon, a miracle occurs!

When monster Booska returns to the earth, he begins a strange life together with Koosaku, a genius inventor who is a high school student.