(Points I could be making)
-The day will finally come when the Universe will stop expanding and will thus collapse in on itself before disappearing completely. Once everything disappears, nothing new can be created ever again
-Kashiko was initially under the impression that she was completely immortal. Billions of years later, she comes to terms with the fact that she’ll only live long enough until the universe deletes itself, in which she will die a slow and painless death in the process
-Unlike Kashiko, Sayori and Sephiroth are immortal to the point that they can survive past the end of spacetime and reality. By this point Sayori and Sephiroth are the only remnants of the once existing cosmos, since everything else would cease to exist, even time itself
-If Sayori and Sephiroth were to die, the only leftover remnants of a previously existing universe would be gone forever from the now cold, deep, and dark void which was once filled with planets, stars, moons, asteroids, galaxies, black holes, dark matter and energy, etc
-In an alternate reality, Sayori and Sephiroth could be tortured just by having to witness several universes/multiverses be born only to die several billions of years afterward, one after the other
-In the latter case, they could make the best of it especially when new species of lifeforms are inhabiting a certain planet and eventually evolve into a new species
