Buta

The two stories seem very similar to me: ❃ There are a map and a treasure ❃ The protagonist is a child ❃ There are pirates ❃ The pirates are anthropomorphic animals ❃ And personally I think that also the atmosphere is similar 

Same duo of a ronin and a boy. A ronin with strange and unusual high skills on combat is recruited by a young boy that's trying to desperatly save his dog.  

Both are adventure anime where the main character is a pig. They are lighthearted and cheerful, with a similar mood and atmosphere. They both also have pirates. The main difference between the two anime is the setting, as Porco Rosso is set in post-WWI Italy, while Buta is set in Japan. 

Both stories are about adventure and heroes. Both animes leave a better impression about charactes