Born in 1566 (though the exact year is disputed) into the Shiga family, senior retainers of the Otomo clan, Shiga Chikatsugu was also known as a Christian daimyo baptized as Don Paulo. In 1586, when a large Shimazu army under Shimazu Yoshihiro invaded Bungo Province (the Otomo-Shimazu War), the 20-year-old Chikatsugu held his home base of Oka Castle with a garrison of only about 1,500 troops. Skillfully exploiting the castle's natural clifftop defenses, he repelled the Shimazu forces in repeated assaults and held Oka Castle to the very end. His conduct in battle is said to have earned him praise from Toyotomi Hideyoshi. After the Otomo clan's domain was confiscated under the Toyotomi government, he became a masterless samurai, but reportedly lived on for many years, dying in 1660.

A young commander of unbreakable fighting spirit who, at just 20 years old, held his ground against an overwhelmingly larger Shimazu army without yielding an inch, combined with a keen tactical eye for exploiting terrain.

Oka Castle, which Chikatsugu defended to the end, is remembered as an impregnable stronghold and today is one of Japan's 100 Famous Castles. Its magnificent stone ramparts rising above the sea of clouds are also said to have inspired composer Taki Rentaro's famous song "Kojo no Tsuki" (Moon Over the Ruined Castle).