Got it, the true evil is slain!
I'm glad we had three weeks since it took me that long to finally try the right thing.
Thanksfully I got all these strong weapons so that I could kill the boss using only my bare hands.
I'm a bit lazy to doublecheck but I think plenty of secrets are actually optional secrets rather than things you mandatorily need to pass by if you want to reach the true ending which is great and the exact reason why I think what you have to do to get the true ending is pretty good, and if I'm wrong about that then it's no big deal anyway.
The game is truly great.