Cpl. Iian Christopher Tarver, 21, pleaded guilty to sexually assaulting the woman in the early hours on Aug. 18, Stars and Stripes reported.
Before the attack, Tarver was out drinking with other Marines and tried to contact his Japanese girlfriend for sex, a Japanese court heard. When Tarver was unable to reach his girlfriend, he grabbed the victim, dragged her to two different locations and forced her to perform oral sex.
Prosecutors requested the four-year sentence, calling the assault a vicious crime.
"The defendant committed the crime only to satisfy his lust, thus there is no grounds for extenuating circumstances," prosecutors said.
Yuji Fujita, Tarver's attorney, sought leniency, alleging that the attack was not premeditated.
"For a foreigner like you, it might be difficult to serve in a Japanese prison, but we expect you to reflect on what you have done," Chief Judge Hideyuki Suzuki said.