They're talking about the stone that our MC got when he killed one of the
"friend" that his brother had. Where he went to save the guys with red hair and blonde hair, remember those guys?
the saber god killed the 4 legendary beasts right
im rlly that not but i think the stone is the black/dark purple ovaled thing that the MC got when he committed genocide to avenge his brother, it was when he was saving the blood sword and the blonde. Also the saber god killed the 4 legendary beasts.
Think of the stone like the philosopher's stone from FMA, it's similar in which it needs ALOT of sacrifices for it to be made and gaining it will give you infinite power
Wait what was the whole reason why the MC kidnapped the saber god’s son again?? Also wtf is this stone they’re talking about