There's Nexton Liquid with Liquid Black Cute, a "dedicated erotic game hardware" it's apparently developing. The price tag is ¥1,107,214,649 or US$13 million.
Elsewhere Illusion, known for its Real Kanojo games, had a set of three "used" life-sized love dolls on sale for ¥1,000,000 ($12,000)—on sale for Apr. 1 only! While another ero game maker, Pil/CodePink, had its "Eternal Magician" peripheral and used a banana to show how it worked.
There are many more adult video April Fools' pranks on 2ch. However, it wasn't only ero game makers who got in on the fun. Capcom Japan said there would be a special idol unit to mark the 25h anniversary of Mega Man—a knowing riff on the idol unit created for Kamen Rider's anniversary.
Everyone's favorite in Japan, however, appeared to be the Google Maps 8-bit prank.
Outside the game industry there were pranks, too. Japanese phone carrier Au, for example, had a special glove phone that could answer calls and throw fastballs.
Yet, not everyone in Japan knows what April Fools' Day is—some do, especially internet savvy folks, but not everyone. Some people, especially older people, might not know the English words "April" (エイプリル) or "Fool" (フール). However, the day is less commonly called "bangusetsu" (万愚節).
That's why April Fools' Day pranks sometimes seem to be labeled more carefully than in the West—usually pointing out the day ("April 1st only!") or featuring a ridiculous price tag. In the West, the pranks are usually played with straight faces as the audience is expected to be in on the gag. It doesn't work as well when you have to explain what April Fools' Day is. (Note: There have, however, been some good April Fools' jokes in the past few years by the Japanese media, but they are usually online.)
That being said, telling the difference between "prank" and "reality" is tough. Some of the erotic game peripherals are too close to honest-to-goodness real peripherals (this, this, and this) that have been released—a wink and a tug is appreciated!