Hoshizora: How is a nightmare defined?

[K450]

I've been replaying the VN in question since a couple of days ago, mostly on the Spica route. During that time,
I've repeatedly tried to pin down the VN's definition of a nightmare, but couldn't find a single definitive passage or
infodump confirming or denying likely conclusions drawn a priori, given the information presented. The questions
I present are thus:
 

From what I understand, the Amatsu-Mikoboshi scythe functions as a conduit by which nightmares of a target pass through the user

and into nothingness. What I presume happens; A volatile copy of the nightmare in question is erased from the target's upper levels of
consciousness, leaving only the archival copy deep within the target's subconscious, of which cannot be sent off by others. During a reap,
the volatile copy passes through the user, giving the user temporary knowledge of the target's suffering, as demonstrated by Mare's reaction
to Altair's nightmare for both instances of reaping. That I can surmise as more or less the general mechanics of the device as far as memories

go. What I am most concerned with is this:

 

• How is suffering defined? Is it an absolute, or is it as in our native world; different for each person?
• If the latter is true, do other scythe users' criteria of suffering also factor into what is erased from the target's upper consciousness?
• Are nightmares more than just possibly bad memories?

 

I wrote down one bit of information during my chronology of the game's story in Spica; nightmares were said by Mare to be,
"Things which people try to overcome but are unable to." Nowhere else is this confirmed to be a general canonical definition.
Mare is after all ignorant, but that's part of her charm.

 

If any of the above are explained in Eternal Heart, please present the most general and non-spoiling answers you can

give. If that proves to be untenable, don't worry too much. The only route I'm concerned with spoilers is Spica, but that's

for another topic concerning some spoilers in that route.

 

 

Cheers!

[Mephisto]

悪夢とは、まつろわぬものの別称だ。

Nightmare is another word for "Matsurowanumono". 

 

それはなにも鬼や神霊の類とは限らない。

It is not necessarily limited to being a demon or some type of divine being. 

 

その者にとって、従えたいのに従わないもの、それがまつろわぬものだ。

As for what that is, a Matsurowanumono is a being that can not abide by the rules even if it wants to. 

 

I think the worst part is that this is the literal etymology of the word, so all the cultural applications of it are lost. 

[Yeah Way]

Even Mare doesn't know. One must simply take it case by case.

 

EDIT: We are talking about "Hoshizora no Memoria", right? There's no one in that game called "Spica".

[yashasupercow]

there are 3 nightmare in Hoshizora if i remember

Mare,the young maiden girl,and the fairy who's following YOU's sister

[K450]

Even Mare doesn't know. One must simply take it case by case.

 

EDIT: We are talking about "Hoshizora no Memoria", right? There's no one in that game called "Spica".

 

That's my nickname for

Yume

I remember Asuho pondering if Altair hadn't gone for Vega, as in the Tanabata legend, but Spica. Editing post when I find the lines in question.