Kurosanji isn't taking out a loan on their stocks. They're moving from a Margin Trading Issues Stock to a Loan Margin Trading stock.
Overview of Margin Transactions | This is the website of Japan Exchange Group (JPX), which operates Tokyo Stock Exchange, Osaka Exchange, and Tokyo Commodity Exchange.
www.jpx.co.jp
Based on the graphs above, it looks like Securities finance companies can now lend out shares to sell on margin which are supplied by other security companies, large shareholders and insurance companies.
So it looks like degenerate gamblers have even more options. Although Riku might be providing his own shares to securities companies for additional yacht maintenance funds as a way to get additional cash without actually cashing out and publicly selling.