He used the curse cast by their destroyed souls to make himself a powerful cursed weapon against undead Osiris (normal weapons can't do a thing to him)
Ya meant jujutsu kaisen ?
Wait but he didn't even know osiris was still alive at that time, remember? He was surprised to see osiris
Oh yea lol
The thing is, Osiris wasn't really alive, the other gods just assumed he was because a dead person wasn't supposed to be able to leave Duat and show among the living... he was only able to be there thanks to possessing Anubis' body (meaning, that Osiris had found a way to repeatedly come back briefly into the world of the living, despite being dead... just as Seth had always known that he would). The other gods didn't know that, so they just assumed he was alive once again (and if Osiris fooled them into putting Anubis' heart in the scale, instead of his, and they didn't realize, then that would explain how Osiris was able to lie and hide the truth so well at that time).
I want a husband like seth but like wtf seth why would you kill those INNOCENT women and children. . stress-relief what. Reminds me of that king of cursed from jenjutsu kaisen (╬￣皿￣)凸