Dōke hyakumanben
A comic Buddhist rosary procession.
I feel like there must be a lot of symbolism and/or jokes here that would be really interesting if I just knew what they meant.
OP said SFW so I wasn’t expecting there to be tentacles. Nope, still got tentacles.
According to some Japanese pages about the image, the five-legged octopus is meant to represent the encroaching “five countries” of America, Holland, Russia, England, and France. The people around them are trying to use a Buddhist chant and rosary beads to fight the foreign influence off.
The big fellow in the back left is a Shouki (in Japanese, the Wikipedia talks about the original Chinese version) and the Japanese source says he represents the Mito branch of the Tokugawa clan while the guy with the Shachi head represents the Owari branch, seeming to indicate that it was a question of which was going to be more useful in determining the outcome.
I think the humans down the right side might be meant to represent the contemporary Japanese, squabbling, and the lord in the bottom right maybe being the emperor of that time? No idea who the people in front are. Probably lots of mini-references.