A giant dog-shaped prototype robot, Yatter-Wan (the name is, naturally, a pun— "wan" is the Japanese equivalent of "woof") sports rescue sirens and lights, iron pellets it fires out its nose, fire hoses on its back, and a horde of mini-robots to help it fight off the bad guys. The dog was built by GAN-chan, a mechanic and son of a famous toy designer who came up with his original design. GAN-chan and his girlfriend Ai-chan join forces with Yatter-Wan to fight the evil Doronjo and her lackeys...and anyone else who pops up causing problems!