In the 2009 DPJ landslide, Ishikawa famously unseated then-incumbent Finance Minister Shōichi Nakagawa.
He allegedly failed to record 400 million yen he and other secretaries borrowed from Ozawa to buy land in Tokyo.
His legal issues led him to resign from his seat in May 2013, when he decided to fully focus on his appeal to the Supreme Court.
He was replaced by NPD leader Muneo Suzuki's daughter Takako, who was next in line in the PR list.
As part of the degree, he conducted a comparative study between the New Labour reforms of British Prime Minister Tony Blair and the DPJ.