Kappas (Water Imps) and humans have a long history together in Japan, and in today's urbanised world, kappas can be purchased as pets. This is what a young man decides to do, and names his water imp 'Kaatan'. With no prior experience of keeping kappas, the new pet-owner consults a 'How to Raise a Water Imp' manual. He cares for, tames, and trains Kaatan, enjoying the imp's charms and patiently enduring his messes! Whether it's potty training or going out to play with other kappas, there's always an adventure for Kaatan and his new owner.