A hero's journey
Sorry, still a fan and here's why. It's not just that Disney always does this, it's that Nemo went on a heroic quest (as did his father) which is time honored delivery of adventure stories. (and there isn't adventure without a little bit of danger.)
Pick up any fantasy book worth it's salt and hero has had some kind of tragic backstory. The biological parents are usually dead or opens with the second one dying. THey don't want to go on their quest but eventually they feel they have to (or are taken against their will until they start acting like a hero) The hero them learns things through a series of harships, has a moment of near death (Or where the readers think the cause is lost), then the happy ending of the quest where the hero and his surrounding are changed forever.
Now go ahead check your other movies. Ailbo baggins goes from living fat and happy in a little garden villiage to sneaking into a cave and stealing from a dragon. Find your own, I'll bet it has most of those elements.