it's kinda confusing but
in ch1 he said he heard a voice and when he woke up he found the swallowing the sky technique, he couldn't cultivate it tho, and then in ch 2 when (i think his name is dao ling? the cousin dude) and the girl take the gem, they try to kill him by making him drink the blood of an ancient beast which just happens to be what he needed to cultivate the technique he found.
basically he found strong technique couldn't do anything with it, murder attempt helped him learn it boom he's strong
hope that helped (ง'-')ง
sounds a lot like SSS suicide hunter. his talent was useless until it was activated by something and then it became powerful
Where did his OP power come from lol I tried reread the first 3 chapters but no clue