@Kickinass queen Yoojin planted the two ss rank mana stones inside his body to create a poison dragon but the mana was leaking and it wasn't developing properly so a fragment of Hyunjae's power or something (his past memory from before mc regressed) infused with the stones in yoojin's body to stabalize the, so now it's developing properly. It's technically also Hyunjae's in a way so yaa, also Hyunjae found out abt the stones when felt the power/mana coming from the stones was similar to his and wasn't rejecting it when he tried pouring some mana into it