Our Bond (2006)

There are three male brothers in the venerable Murano family. His eldest brother made a vow with his father to keep the traditional Murano family alive, but he knew best that he couldn't keep it... The second son, Tamakichi, enjoys nothing more than going to the mountains or rivers and masturbating naked. He relies on his third son, Kuniyoshi, but one day, he brings his girlfriend, Yonemura, to Sakuzo and proposes to marry him. Moreover, Yonemura is a man. Is Sakuzou flustered...?