Each film has a certain kung fu style or a goal that Po must achieve, and in this one he has to master the Chi while at the same time learning to know what it means to be a panda. Po's long-lost panda father reappears, just as the supernatural villain Kai, from the spirit realm, returns to the mortal world and vows vengeance. We know that it was just a matter of time until Po reconnects with his family, it was teased at the second film's end. But being a teacher is not Po's only new challenge. But that's the thing, once you've felt comfortable and you do only what you can, then you close any room for growth. In KUNG FU PANDA 3, Master Shifu appoints Po as the new teacher, a responsibility that of course Po is not able to handle, because he feels more comfortable just being the dragon warrior that saves the village whenever they need help.
There's a reason why the 'Kung Fu Panda' franchise is one of the most successful of all-time, and I'd like to believe that that reason is because the writers and the creative talents behind it know how to solidly move the story forward, even with the same characters, they know how to make them evolve without losing the charm and the heart that made the first and the second film effective.
