From the introduction:
Konagai Yuuko is a young highschool student, struggling to make friends and living an ordinary life. She also happens to have three cats-Maa, the mischievous munchkin, Shii, the gentle Singapura, and Rou, a sensible Russian Blue. Her life practically revolves around these three cats, and they love her in turn.
Soon she’ll be making a couple of new friends as well in the super-rich Shiratori Azumi and her pet cat Elsa, and Azumi’s self-proclaimed rival Iketani Ran who is deathly afraid of cats.
She will get into a number of funny situations, ranging from struggling in school athletics, trying-and failing-to learn to cook, and more. In the meantime her cats will have adventures of their own, pretending to be humans, trying dieting and fashion, or escaping the house to go visit an aquarium.
In truth though, this is a very calm and peaceful world. Cats just so happen to look like excessively tiny humanized catgirls, which marks the only real change from a perfectly mundane world. There are no climactic battles, strange mysteries, or horrors to defend against. It’s just...cute girls and cute cats doing cute things.
Savor this break, and have a few happy Nyanko Days.