Story: Long story short, it's about a 30 year old bachelor who adopts a six year old girl named Rin. Those are roughly the ages but a simple premise leads to one of the most heartwarming and adorable series I've ever had the pleasure to watch. It's strictly slice-of-life and doesn't devaite from it with any fancy, wacky sci-fi fantasy whatever elements, and since it's just everyday stuff, it should be tame and boring but it's fun and so endearing that it's captivating. It's not simply Daikichi taking care of Rin, but also the other way around sometimes, and both of them learning, especially Daikichi, what it means to take care of/being a kid.
It's unbelievably adorable, and may cause your heart to explode in rainbow bunny fluff. The everyday mundane stuff is made cute with "Dawwwwww" moments throughout, and that's the main charm of the series; seeing Daikichi and Rin go through with their daily ordeals.
Animation: The beginning of every episode features a style different from the rest of it and that beginning, is so gorgeous that there was no way they had a budget for it. So artistically beautiful that you wish that the rest of the show was the same style. Unfortunately, the rest of it doesn't compare to it but still looks the part with it's simple, peaceful glory. No heavy black lines or stylistic shading, it's perfect and enhances the adorability of everything.
Sound: Massive props on not making Rin's voice annoying and just enhancing the cuteness. The other voice actors are great, the OP/EP are pretty good and the sound just compliments it overall.
Characters: This is the bread, butter, muffin, orange juice and cheese danish of the anime breakfast. It's about Rin and Daikichi, their interactions, their routine, their everything. It focuses on them, has them at the centerpoint and they are the best part of the show. How Rin goes from distant at the start to an outgoing, smiling girl, and Daikichi from his bachelor status to a full-fledged parent, the journey they take, it's... it's just beautiful. Their development is as perfect as can be and the side characters compliment them and help them grow, which is as good as it gets.
Overall: Watch this for Rin and Daikichi and how they grow and adapt. This is without a doubt, one of the best slice-of-life anime I've ever seen in my life, or will see. Amazing on so many levels that the only problem is that it was only 12 episodes of majesty. And one of the most adorable things I've ever watched, to the point where I cried because it was so heartwarming.
I'm not kidding on the adorability.