On a strategic and technical level? Against the Americans (after obvious early land grabs), they were. The US was trying to get to the Japanese home islands, and the Japanese were trying to defend them. So at the most basic level, at that time it was a defensive war. However, that ignores the larger context surrounding why the Japanese had to defend against the Americans(hint: it involved blowing up the better part of the US' Pacific fleet and occupying their colonies). And none of that even touches on the Japanese invasion of China and attempts to create a East Asia Prosperity sphere by subjegating their neighbors. So, yes they technically fought a defensive war in the Pacific, but A; the context surrounding it justifies the attacks against them, and B; They also fought a brutal offensive war. Sorry about formatting, this reddit app confuses me, and if this answer isn't in depth enough I can add more to it once I get home to an actual computer.