Dashing Student - Chapter 705, The Backer Behind

Xia Yan passed through to the world of Bleach and became an eleven-year-old boy. He was rescued by Renji and Rukia in the Seireitei, and he was studying at Shin’ō Academy, and he was a student of the same class.
He is a top student of the Shin’ō Academy, and he is vying for strength by various teams. In the end, he has entered the first team of secret mobile maneuvers.
He will use punishment to kill every person who tries to threaten the martyrdom and protect his loved one.

- Description from Novelupdates

Struck down amid the battle, the Hero and Demon King meet their demise. As their souls linger on the edge of the afterlife, a mysterious force intervenes, merging their fragmented souls together with a new being. Rusty, the living armor, now affected by their memories and presence, embarks on his own quest. Will he seek revenge on those who betrayed the hero, or will he fulfill the desires of the fallen demon king? or instead, forge his own path?

My name is Kaelith Yurei , and I am a first-year student at the Shin'ō Academy in the Soul Society. I have a friend who is destined to be quite famous in the Soul Society; his name is Sōsuke Aizen.Unlike this ambitious and idealistic friend, my goals are quite simple: through hard work and diligence, I aim to graduate and become a seated officer in the Gotei 13, from which point I will… I bounded with who!?Whenever Aizen enhances his strength, my power automatically synchronizes to match his level.Therefore, what I need to do from now on is very clear.“Sōsuke, you need to work hard. As long as you put in enough effort, I can live the life I desire!”