[Hoshizora no Memoria: Eternal Heart Translation Project]

Well based on what I remembered Mare was basically the "Child" the MC and Yume "had". They both wished upon a star or Yume did and because of that wish Mare was born, but a part of Yume, I'm guessing like her life energy or something, was used to give birth to Mare. Which is why the only way to save Yume was for Mare to sacrifice herself thus returning the "Life Energy" that was taken from Yume back to her. Which saved her life.

 

Ahh, i see.. well that explains i guess... thanks for replying!! xD 

[Hoshizora no Memoria: Eternal Heart Translation Project]

Alright keep it up steve!! looking forward to it.

*Btw, Can someone explain to me why did 

 had to sacrifice herself in order to heal yume's disease?? i didn't get it, it's kinda ambiguous for me