If you're looking for anime similar to Kappa no Coo to Natsuyasumi, you might like these titles. All recommendations are made by Anime-Planet users like you!
Satsuki, her younger sister Mei and their father have just moved to their new home in the countryside, where grand adventures await them. One day while playing outside in the garden Mei encounters a small creature and decides to follow it. After chasing it through the bushes Mei eventually finds herself at the base of a large Camphor tree and as she drops through a hole in its roots, she lands on the stomach of a large, sleeping forest spirit named Totoro. The two sisters befriend the gentle spirit and are soon introduced to a world more fantastical than they could ever imagine, from playing with soot spirits to meeting a Catbus, to flying through the air and even making the trees grow. However when Mei disappears, Satsuki must call on the help of her new friends if she wants any hope of being able to find her sister...
The main focus of both of these films is the friendship between a young child and a supernatural creature. While Totoro has a more light-hearted nature to it, noth show an everyday adventure with a supernatural twist. If you enjoyed one it is worth at least trying the other.
A boy arrives in purgatory after dying, where he is informed that in his past life he committed a terrible sin, and cannot be reincarnated until he can remember what it was. Until he does, he is placed in the body of a middle school student named Makoto who committed suicide three days ago, and is instructed to live the deceased boy’s life. New Makoto quickly becomes fed up with his host body's situation, as the boy doesn't have any friends, his family life is in shambles, and his mere presence makes everyone around him nervous. But giving up is not an option, and if the spirit ever wants to move on, he must adjust to Makoto's life and understand what happened in the past.
Keiichi Hara's Colorful was one of my favorite anime films of the last few years, but don't overlook its predecessor, 2007's Summer Days With Coo. While it doesn't have the complexity of Colorful and the animation is clearly a couple of levels below, Hara packs the same narrative skill and unerring eye for family dynamics into both films.
Don't be fooled into thinking "Coo" is a light, cheery family film. It's a pretty dark story full of difficult themes and rather dim views of the human race. As is Hara's style, however, the movie is ultimately optimistic in its take on the ability of good people to affect good results. Clearly influenced by Miyazaki, "Coo" is less refined but more gritty than the master's films. Highly recommended.
As to "Colorful", it's quite simply one of the best theatrical anime of the last half-decade. This is a serious, thoughtful movie that pulls no punches - dealing with topics such as teenage suicide, enjo kosai, and bullying. Hara takes pains not to sugarcoat his hero into a sweet, lovable cherub - Makoto is a complicated, difficult teenager whose path to darkness is portrayed with startling realism. Yet ultimately, the film is life-affirming and hopeful in a thouroughly Buddhist way.