Bleach: I'm Bound to Aizen

My name is Satoru Mikami, a first-year student at the Shin'ō Spiritual Arts Academy in the Soul Society. I have a friend—someone who, in the future, will become quite famous in the Soul Society. His name is Aizen Sousuke. Unlike my friend, who is filled with lofty ideals and grand ambitions, my goal is simple: Graduate through hard work, join the Gotei 13 as a seated officer, and live a stable, carefree life as part of the warrior class. That is… until one day, a strange thing called the Binding System appeared. Its rule is simple: Every time Aizen improves his strength, my strength automatically synchronizes to the same level as his. From that day forward, my path became perfectly clear. "Sousuke, you've got to work hard! As long as you keep pushing forward, I'll be able to live the easy life I've always dreamed of!" — Description from novelcodex.org