Ooh, the Eastern sea's so blue...dammit!

It's a little distressing how quick Uncle Grandpa is to pronounce his friends dead. The mere sight of a graveyard in Giant Realistic Flying Tiger's path convinces him that she died in "Tiger Trails" , and in "Big in Japan" he's making funeral arrangements the moment Mr. Gus hits the ground. I guess if you've been around long enough to be an Uncle Grandpa (or perhaps are ancient enough to be a genie, that's a rabbit hole to explore at a later date), you've had enough loved ones die on you that you've come to expect it...wow, that's grim. Like, Season 3 Adventure Time grim.
As for the episode proper, "Big in Japan" sees Uncle Grandpa and associates take on another old standard, the kaiju episode. So far, it's been a general rule that the more screentime Mr. Gus gets, the funnier the segment, and this is no exception. Fortunately, the entire episode isn't just devoted to the inevitable visual of Toho-style urban renewal, which was already addressed pretty thoroughly in the "Workout" short. Events eventually segue into Mr. Gus' awful faux-funeral - again not the most original situation in all of animated comedy, but the unintentional roast works in many of the ways the "standup" sequence in "Perfect Kid" failed to. This seems to be where Uncle Grandpa works the best - taking on traditional cartoon plots and adding a layer of surrealism and a few good lobs at the radar. That's been enough to sustain Spongebob Squarepants for an inordinate number of years post-movie - and it still provides more comedy per episode than any other current Nickelodeon fare in spite of itself. Uncle Grandpa falters, though, when it imitates Spongebob too closely, or runs with a stock plot and doesn't do anything that actually requires its own characters and world.
On a much more minor note, this episode also contains a particularly stark example of a running gag sent straight into the ground. "Ac-TOR" was funny the first time (and even then mainly because of Gus' 'theatrical' hand flourish) but it did not improve on repetition. By the end of the episode, I was well into "oh, just say it right!" territory. Kudos for the title pun, though. Ouch.

Transitioning awkwardly, I'm not sure if this is a skillful sidestep of the treacherous area of ethnic caricature or walking right into it - other than a marathoner, businessman, John-K-esque ingenue and a mandatory geisha, all of whom we see for a few frames at most - this one child seemingly comprises the population of Tokyo.

Other than this run-through crowd - even at the  blockbuster movie premiere or as Mr. Gus rampages through a major urban area - we see one character outside of the regulars. Perhaps there's an Ocean justification in effect to keep everything TV-PG or lighter, and all those buildings were empty because it was Sunday.