Damn It! I've Become the Guardian of the Original Villains

[Title: Damn It! I've Become the Caregiver of the Original Sins]

[It's a password, I mistyped it...]

[Nearly Invincible + Incubus Male Lead + No Angst + Every Character in the Book, Male or Female, Could Be a Love Interest, Depending on Reader Preference + Yandere]

I, Kane Kalia, am the “Saint's Child” born into a family of saintesses.

No, no, what I mean is that my younger sister, Ia Kalia, is the real saintess.

I'm just her brother.

But what if there's a chance...

That this world, in [my] eyes, is just another story?

A story in which I was never supposed to exist.

And yet, as a member of the Saintess family, I'm secretly raising the “Original Sins”!