Forty years ago, a boy named Yukinari saved the deity of the forest, Celebi, from a Pokemon poacher's hands. However, Celebi used its time traveling abilities in the scuffle, and transported both itself and Yukinari to the present! Ash, Brock and Misty find the duo and with the help of Celebi, Yukinari is soon on his way back home - that is, until the sinister Iron Masked Marauder arrives. He's on a mission to capture Celebi, and he has a "dark ball" capable of turning anything it catches into evil. Joining the fray is Team Rocket, who also want to get their hands on Celebi. An ultimate showdown awaits, and the entire forest is at stake!
With the rise of the Iron Age in feudal Japan, man and nature grow increasingly at odds. As mankind infringes more and more into the kingdom of the beasts, many of the elder animal gods begin to succumb to their rage, cursing themselves as they lash out at rural and urban settlements alike. When a young Ashitaka, hero of his village, is imparted with one of these curses after slaying a crazed god, he forces himself into exile to prevent further harm to his village. As he ventures out into the world, however, he discovers just how dire the straights have become - with man and beast ready to break into all out war, his curse becomes the least of his problems. As both sides teeter dangerously on the side of outright slaughter of one another, Ashitaka sets his own problems aside and, using his charisma and honor, seeks to quell the hatred before it gets beyond repair - but will he be in time or is he simply delaying the inevitable?
Now, normally I wouldn't recommend an intelligent classic for anything Pokemon - but Pokemon Movie 4 and Princess Mononoke are truly two peas in a pod. Sure, Pokemon Movie 4 is aimed at a younger audience, but both are titles that speak strongly against disrupting the environment. A forest deity is targeted in both, and the deity ultimately is in the position of destroying the forest itself. Give it a try.