Service, Duty
You loiter around with a weapon because you're currently doing your service and duty to your country. You're standing guard outside, waiting just in case something will happen.
Imagine standing around with a weapon in your hands. It feels more like you're doing nothing, loitering around the wall, but this is how you offer your service to your country, so you have to do it.
やく, えき
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You're about halfway through your service, when a yak (やく) walks by. It stops directly in front of you and grunts. "Excuse me, Mr. Yak, but it's my duty to escort you away from my country."
Somehow your duty has become pushing this stubborn, hairy yak away from the entrance to your country. You poke it in the butt with your weapon, but it doesn't seem to care.