Arc System Works created a DSiWare game starring Chimaki, a hidden character in Guilty Gear 2: Overture. The goal in the game is to get the towel-slapping hero to a legendary hot spring to relieve his back pain.
Aksys picked up the game, but it appears they aren’t using the Guilty Gear branding. The game is known as Fura Jump: Guilty Gear Gaiden in Japan and Towel Slappin’ Pro-Jumper! in North America. The ESRB spilled the beans with a rating and this description.
This is a side-scrolling platformer game in which players guide a small pillow-like creature through a variety of "cartoony" hot springs. As players run and jump through levels (some depicting male characters wearing towels inside hot tubs), they defeat various turtles, frogs, and pink elephants by slapping them with a towel. Enemies disappear in brief puffs of smoke when hit, and the central character reacts to damage by blinking and falling off-screen. The names of some levels are based on innuendo and puns (e.g., Nude York, Rome Laid Bare, and Full-Frontal Fuji), and one leaflet contains text that reads, "For help with . . . un-natural male enhancement."
Nude York? Full-Frontal Fuji? Those totally sound like Aksys jokes. If you’re curious, there’s a wacky trailer of Towel Slappin’ Pro-Jumper! to watch.