It's about parenthood. Souta unexpectedly becomes the father of Poco, who's a typical three-year-old boy. The show's walking us gently through Souta's experiences as a dad, just like anyone else with a young child, but with the extra dimension of Souta's own issues with his late father. It's a charming series and I think you could show it to anyone.
There's a minor twist, though. Poco isn't human. He's a tanuki, i.e. a chubby raccoon dog thing. Japanese folklore says that they're shapeshifters (like foxes), but that's not important most of the time. Poco's not just pretending to be a tiny boy. He really has about that much brainpower, i.e. he's very affectionate, doesn't understand much and has only an approximate grasp on human language. You could make this an entirely real-world series and you'd only need to change a few scenes here and there. Being a tanuki is only a problem when Poco loses concentration and grows furry ears and tail.
The show's foreground is Souta-as-dad. He moves back to Udon, Kagawa (aka. Hicksville, Rural Accents-a-Go-Go, Middle of Nowhere) from Tokyo to sort out family things after his father's funeral, only to find Poco in a field. Suddenly he's a surrogate dad. This isn't what he'd planned, but he tells everyone he's looking after a friend's child. He makes "Mum Friends" with an old crush of his who has two children. (She gives him parenting tips and they help look after each other's children.) He discusses things with his older sister, who'd decided not to have children herself. He makes everyone worry about his work situation, since he's staying in Kagawa far longer than expected and not answering work phone calls. (He's a web designer and you'd think he'd just arrange to work online and dial into the office, but I can imagine that not going down a bundle in a lot of Japanese companies.)
There's no romance in the show, although admittedly that's to the distress of one character. The story's not about that. Its cast are thirty, not twenty, and the show's exploring entirely different themes. Plenty of them are already married. (It's possible to play "spot the potential love interest, maybe, one day", though.)
There's even a show-within-a-show, called Gaogao-chan and the Blue Sky. Poco watches it on TV and goes to Gaogao stage events. What's more, we see it every episode as a little kiddie bit after the end credits. It's kiddified silliness and the kind of thing you're liable to find on your television if and only if you have a small child, but it's also liable to be a thematic reflection of what was happening in the main episode. (Gaogao-chan is a lion-like alien who came to invade the Earth, but is actually friendly and has best friends called Mimi and Momo. He also has a zipper up his back.)
In the background, though, is the mirror image of all things Poco. That's Souta-as-son. His father ran an udon restaurant, but Souta came to hate Kagawa and hate the idea of becoming an udon chef like his father. The restaurant's now closed, because Souta refused to carry on the family business. What Souta learns from being Poco's surrogate father will give him new insights into his own family relationships, but unfortunately too late.
It's a heartwarming show. It's also emotional, in its gentle way, but not in unhappy or surprising ways. It's almost exactly what you'd expect of a sympathetic, well-observed story about a parent and a child. The cast isn't large, but they can all feed into the story's themes, since everyone has a parent. Nakajima, for instance, is both Souta's childish old friend and a career-driven single man who has problems with his father (who wants him to inherit the family business: a hospital) and his mother (who wants him to get married). The show's an easy recommendation. Not only did I always enjoy it a lot, but I'd struggle to imagine anyone not doing so too. It's happy, relaxing and easy to watch at any time. My son's about that age and its portrait of parenthood rang true to me. Admittedly the ending's more complicated emotionally, since Poco's really a tanuki, not a boy, but it's still a feel-good show and one of the nicest anime of 2016.