Bleach: My Zanpakuto Is The Almighty

Overworked wage slave Li Mo dies suddenly after another late night at the office, only to wake up as Ichigo Kurosaki from Bleach! Faced with roaring Hollows and the tiny Rukia, he thinks he's landed in a hot-blooded battle manga and gets ready to power up and charge through everything.

But something seems off about his Zanpakuto, Zangetsu. The moment they meet, it whispers in his mind:

"Master, Old Man Yamamoto's swordsmanship, hand-to-hand combat, and Kido are outdated. The power of a Soul Reaper is, at its core, whatever the heart imagines and the body can achieve... Come on, I'll teach you how to exploit this world's bugs."

From then on, the whole atmosphere of the Seireitei goes completely off the rails!