Japan needs us as a counterweight to the billion-and-a-half people across the Sea of Japan who hate them with the intensity of a million suns over what they quaintly called the “Greater East Asia Co-Prosperity Sphere”.
Admittedly, the Chinese people have historical reasons for antipathy toward Japan. Not excusing Chinese aggression now, but there's a lot of hate over there to go around.
Chinese have a good reason to hate Japanese.