Oh, that? It's 妖気(ようき) youki lit.ghostly; unearthly; weird. I left it like that since I'm still unable to find the right word for that in English, sorry. I'm guessing it's "youkai power" or "youkai energy" or something along the line, not sure. -_-
That last bit of the monologue could be in reference to flowers, how they bloom and wilt in a few months time.
"From the start, she was not born to live a long life...""...too weak and thin even to try prolonging it."We do not "grow".And I'm not the Sun.Yes, yes, of course not.After all, even if Jupiter couldn't become like the Sun, it could continue to exist as a planet."...and very little time."However, that is not the case with her.She's an unstable vessel of mystic energy that could not become you....and I'm afraid that—That Moon doctor said so, too."A small vessel, weak power...""Those are all she has."...This girl isn't a planet....Her power will keep weakening......I already know about it.