Complex sentence: Yoshikazu was a kindhearted gentleman who worked at Heavenly Host and generally got on well with the students before he became Sachiko's puppet, where he helped her perpetrate the murders of 1973 before he took his own life.
Split into simpler sentences: Yoshikazu was a kindhearted man who worked at Heavenly Host and generally got on well with the students before he became Sachiko's puppet. He helped Sachiko perpetrate the murders of 1973 before he took his own life.