Okay I'm no expert and I don't know anything about the "Japanese coast guard" but why can't a coast guard officer have permission to use a firearm? the US coast guard carries weapons and is a branch of the US armed forces. I'm not an expert but I would assume the Japanese coast guard is apart of the Defense Force which has training and carries weapons.
It's also stupid they reported unidentified creatures attacking killing 2 and critically injuring 1. Yet, they refuse to send any kind of help. Also, why are they looking for a crashed airplane without using helicopters.. I need to stop trying to rationalize this and just enjoy how B movie it is.