Thirty Days to Win His Wife(2016)

Daifuugou no Sanjuu-kakan no Kyuukon

Amelia's best friend Tyler suggested on the night of their high school graduation that they get married if they were still single when they were twenty-eight years old. She didn't believe it'd ever happen... Ten years later, at their reunion, the duo get tired of their friends bragging about their families and sneak out into the Las Vegas night. The next morning, Amelia can't believe her eyes. Tyler is sleeping naked next to her! She then remembers what happened the night before-they'd gotten drunk and married one another at a local chapel. Later when Tyler learns about Amelia's pregnancy, he says they should live together to decide whether to stay best friends or become a real wife and husband!

(Source: Renta!)