At first, Sorin protected Christians for the purpose of trade, but he was soon attracted to the doctrine of Christianity, and finally joined and caused the Battle of Mimi-kawa while dreaming about building Mushika (ideal world, represented as 務志賀 in Chinese characters, around present-day Mushikamachi, Nobeoka City, Miyazaki Prefecture) in Hyuga Province.
当初は貿易目的のためにキリシタンを保護していたが次第に宗麟自身もキリスト教の教義に惹かれるようになり、遂には入信し日向にムシカ（理想郷。漢字表記は務志賀とされる。現在の宮崎県延岡市無鹿町の付近）の建国を夢見て耳川の合戦を引き起こすことになる。