There are 3 world of different level. Mc master got poison in the highest world where his GF got kidnapped,so his master came to lowest world to recuperate where he meets mc and train him, Mc gets an inheritance where he cures master who returns to highest world for revenge. Mc says to master to stay alive otherwise he would kill all when ascending at the third world to take revenge for master
Pretty sure this was on Royal Road like... 5 years ago. He got trained in some kind of steel body martial art and learned potion-making on the side, because xianxia. Got dropped after a couple dozen chapters or something.