what that dark spot REALLY is, is caused by the japanese.
ya see? they have waayyyy too many monsters over there. ultraman's been having to work overtime. and if you guys remember, he gets his super powers from the sun.
so if japan would stop breeding silly things like mothra, and other gihugic insect looking monsters, ultraman could take a break, and the sun would be fine.
they fired the space giants, because they couldn't pass emissions. johnny socco's giant robot became too expensive to repair, and his nuclear power source couldn't be renewed. godzilla finally realized that those silly humans were just using him, and retired to a quiet mountaintop. this left ultraman overloaded, and he is killing the sun.