The manga focuses on Ginjirou Manda, a loan shark businessman connected to numerous Yakuza gangs in Osaka. He applies an interest rate known as toichi—adding 10% every 10 days, totaling 365% annually. Due to his relentless debt-collection methods, he is dreaded as "Minami no Oni," or the "Demon" of Osaka's Minami business district. Even when borrowers attempt to swindle him, he invariably finds a way to recover his funds.