I don't know, and probably no one else does either, and I've been following manga for years
Ferid amd Guren work together because they want to revive everyone dead. Yuu's dad (the first) who's basically Shinoas Demon tried that first since they got send from heaven to earth as punishment for the first creating yuu. So basically they all died on earth because the air is contagious and he tried reviving which resulted in a catastrophe which only worsens, guren tried to fix fhat with mahiru and ferid joined. So Shinoa is against that and Yuu wants to follow the rvival plan because of Mika and the Orphan kids and now they all mad. End.
Can someone catch me up on what’s happening lol like last I saw was the end of season 2 anime