The 67-year-old former defence minister narrowly prevailed over hard-line nationalist Sanae Takaichi in an unpredictable race with a record nine candidates to lead the Liberal Democratic Party.
The yen rebounded against the dollar on Ishiba's victory after falling on news he would face the run-off against Takaichi, a monetary dove and fiscal expansionist.
A monetary hawk, or hawk for short, is someone who advocates keeping inflation low as the top priority in monetary policy. In contrast, a monetary dove is someone who emphasizes other issues, especially low unemployment, over low inflation.
Japan has struggled with deflation for decades. Inflation has been a welcome development for them. With an aging population and low birth rates, they aren't in danger of heading into hyper inflation.