If Kamikochi is my last place of travel...

Hi,
Well to be honest that's not the ideal place to end up. Your only real choice is to take the bus to Matsumoto and then the train into Tokyo (preferably leaving from Haneda Airport) or taking the bus to Takayama and then trains to Centrair Airport via Nagoya.
I did not check airlines, fares or routes. You could do it from either, but I myself would choose Nagoya.
One thing you can do is when you get to Kamikochi, go to the Kamikochi Visitor Center and ask. They will have the schedules and other info.

Good luck.