As Masamori contributed his domain in Iga Province to the Retired Emperor Shirakawa, and was appointed to important posts, such as kebiishi (a police and judicial chief), and Tsuibushi (envoys to purse and capture), whereby he assumed responsibilities for subduing and apprehending local bandits across the various Provinces, etc.
また、白河上皇の院政に伊賀の所領を寄進するなどして重用され、検非違使・追捕使として諸国の盗賊を討伐するなど活動した。