We all know about the bouncy breast physics in games like Dead or Alive - but what of the games that are considered too esoterically lewd and dodgy to ever be released outside of Japan?
Here we round up just a few of them...
Surreal and bizarre, the series reached peak oddness with Kyuukyoko Muteku Ginga Saikyou Otoko (roughly translating as "Super Big Brother - The Ultimate Most Powerful Man in the Milky Way").
Backgrounds and enemies were digitised sprites comprised of muscular, naked men (such as the pneumatic monstrosity above, or a wall of bare boys kneeling on one another's backs). Notably, your ship would transform between stages, sometimes depicted as a spinning nude in tiny pants, or - for some reason - God: the most super Big Brother there is.
Described by its developer, D3, as an "open world high school love adventure", it happens to be an open-world high school love adventure which stars a wretched pervert.
Set on an open-world island, the main character is set tasks by a local "journalism" club, which typically requires him to take photographs of young girls' underwear. Sometimes, knocking them to the ground would reveal your target's knicks, or you could slither between the legs of someone while they were chatting, or hanging out at the beach in a tiny bikini.
One token concession to morality and legality was made: if you got caught, you would be taken into police custody, or sent to see the school counsellor. The jaunty title song, soundtrack, and cutesy graphics watered down what is - whichever way you look at it - one creepy and shady game.
Nevertheless, it was no niche release, and proved to be a sizeable hit in Japan. And yes, there is a turtle coming out of the girl's bottom.
In gameplay terms, it resembled the TV game show Hole In The Wall, albeit with less Dale Winton, the mahogany hunk; the thief would smash through buildings, and the player was required to contort themselves - with the help of the Wiimote and nunchuck - to fit the shape the thief left in his wake.
Though not all the characters were oiled muscle men in tiny posing pouches - there was also a female bodybuilder and, inexplicably, a "cheerful polar bear" - most of them were... with their toned buttocks jiggling salaciously as they ran after their quarry.
Released by Namco, it's a long way from Pac-Man.
As each platform stage ends, the player is required to make moral decisions which affect the path of the story - as Vincent is confronted with the news that Katherine has missed her period and may be pregnant, her attempted suicide, and managing his alcohol intake (which affects his performance in the levels).
Not quite as shameless as some of the other games listed here - it is nevertheless shows a boldness on the part of Japanese game developers to tackle subjects that the West typically shies away from.
Though beat 'em ups aren't strangers to homosexual characters - traditionally insensitively depicted as weird bosses (see Streets of Rage 3's outrageously camp and preening Ash, for one example) - Vendetta is the only documented beat 'em up where the character is repeatedly dry-humped by leather-clad oddballs.
Weirder still, when left to their own devices, these bare-chested opponents are so overcome with lust that they will also attempt to hump streetlights into submission.
Why? Because he gets sexual gratification from being verbally abused by them. Which sounds like an attempt to disguise the dubious nature of his actions.
It's basically the schoolyard game of statues as played by an ageing degenerate: if your prey turns around, you character has to stand stock-still. Drinking alcohol gives him the courage to move faster. And if that isn't sending out the wrong message to easily influenced idiots...
His aim is to find true love before the effects of Cupid's magic wears off. And he does this by keeping wave after wave of girls at bay by shooting them with "pheromones" - which causes them to drop to their knees in a sort of loved-up stupor. Camera angles make the most of short shorts and shorter skirts - because looking at your teenage classmates' knickers is acceptable when one is looking for true love, apparently.
In short; Jesus, Japan...!