The world through a cat's perspective is limited to the colors of blue, yellow, black, and white. Due to this condition, the feline Hachi has found life monotonous and remains apathetic at school. In class, his attention always drifts away, but a new transferee may be able to shake up his tranquil world.

Being in a student body full of furry animals, the lizard Aoi is someone fresh and interesting to everyone's eyes. He is intelligent, mannerly, and wears ample clothing even in the summer. Despite the new kid on the block, Hachi initially does not waver. However, a chance encounter soon leads Hachi to witness Aoi's secret: his tail emits a wholly different shade—a color Hachi has never seen before.

As he observes Aoi's brightly twinkling skin, Hachi stands in awe and desires to see this hidden spectacle once more. The two exchange their personal wishes, and soon Hachi's monotone blue life shifts into a vivid blue.