"
Looks to me like two open-ended pipe bombs powered by either black powder or some similar fireworks pyrotechnic substance."
A homemade muzzle loader with electric igniters of some sort instead of caps. The amount of smoke in the
video shows that it was probably black powder.
"
Is that a holstered REVOLVER on the hip of the security agent?"
Yes. Standard for security and police in Japan last time I read about it (quite a while back).