Hello guys, I remember a part of a novel in which the mc wanted to learn a body strengghthening technique, so his father made it so many masters came so he could choose the one he thought would be best. I remmember most of them only strenghthened one part of the body (like, one only his fists, which allowed him to break rocks with his bare hands) but one of them, who I picture as really thin and wearing black (I'm not sure if that's how he was described) strenghthened his whole body, but I think his training method was a lot harder. I also think he only agreed to teach the mc for a fixed time period, after that he'd leave. The mc (obviously) made the deadline and learnt everything.

think you can help me find the novel? Thanks 🙂

Stellar transformation

that's it, thanks