They simply – had the ability to see.
Apparitions.
Ghosts. Ghouls. Spirits.
Specters – phantoms.
Questions of proper nomenclature aside, the Sacred Guardians of Mt. Shirei had the ability to see people who were dead and gone.
They call it – necromancy.
It may sound crazy – but remember Kyoken Maniwa, who waylaid Shichika Yasuri and Togame the Schemer last month on Mt. Odori? How could she have taken over thousands of bodies over the centuries without something like a soul to do the work?
This was about – persistent presence.
While there may not be an afterworld – there is a dreamworld.
And the presence of memory.
Is the presence of the departed.
The presence – of dreams.
Along those lines, consider the Infovac of Maniwa Kawauso, “The Nosey Otter.” It may come across as superstition, but perhaps it has some philosophical basis after all. Furthermore, while Kawauso Maniwa was from Maniwa Village, born and raised, his father’s side had roots in Mutsu – so they say.
You can imagine just what Princess Negative would declare:
“There’s no such thing as ghosts – but I don’t doubt those men can see them.”

Katanagatari Omnibus 3, Page 62