It's such a simple story and it works so well. You got the fake dating trope which in this case is 'fake marriage'. Anya, the kid character, is not one of those whiny annoying kids and is actually very funny, likeable and believable. You don't have to worry about any weird scenes you typically have in anime like panty shots or unnecessary fanservice, it's very family friendly and wholesome. The characters and plot are interesting enough that you're not bored, this isn't a slice of life anime. It's got action, tension, comedy, romance and my favourite: the found family trope. Can't get enough of it, new comfort show.