Since the original Hantegu backstory OST is not any where to find yet,
I extracted the backstory theme from the final episode as good as i´ve been able to and mixed it with "Pharozen" and "Diego Mitre Music" cover versions of the final battle theme.

All rights/Credits to their respective owners:
‪@pharozen‬
‪@DiegoMitreMusic‬
Original Demon Slayer composer: Go Shiina