Blades of Unity: Demon Slayer Chronicles

In a world cloaked in darkness, demons prey upon humanity under the veil of night, while demon slayers rise to protect the innocent. But when an advanced alien civilization sets its sights on Earth, intent on obliterating all life, a new chapter unfolds. Former adversaries must forge an unlikely alliance, setting aside centuries of animosity. As the fate of the world hangs in the balance, can demons and slayers overcome their differences and stand united against this existential threat?

Kagaya Ubukuyashi: "The foremost duty of demon slayers isn't merely to exterminate demons, but rather to safeguard humanity. Even if it means allying with our sworn enemies, we must prioritize the preservation of human life above all else."

Muzan Kibutsuji: "It is a matter of simple logic. Should the human race face extinction, so too will the demons perish. However, in this alliance, we shall reveal to these interlopers the true essence of demons and the power that lies within us."

There will be references from other anime as well and they don't belong to me.

I don't know if this idea is stupid or not but I just got inspiration from a movie.