Why does Bermuda always address characters as -kun?
In this case I believe Bermuda is looking down on all the characters as if they were his subordinates or just addressing in an endearing sense (he is way older than them).

In company or school situations in Japan "-kun" is by superiors when addressing subordinates of both genders. Alternatively "-kun" might also be used as a term of endearment towards the (younger) male characters (similar to "-chan" with females).