It gets worse when you find out more about Nia—-the parallels to Senia are drawn, but Nia dies at the end. No wonder Magaleta sought out the Tower of Eternity.
The scenes where Nia falls sick and cannot be cured. Up until she dies, Magaleta forces herself to lie to Nia just so she can keep her smiling, knowing deep down there's no hope for Nia.
"I had a dream. Daddy and mommy were in it, but you weren't there. I searched for you everywhere, but you weren't there. Mommy said you weren't supposed to be there..."
"Daddy and mommy are calling...I have to go..."
The endings:
Ending 1, when you defeat Magaleta's first form without having the cross pendant equipped. Magaleta consumes Senia with the Eternity. At first, Senia tearfully objects, but over time, she grows silent and accepting of her fate; at least she's together with Magaleta. The title drop at the end drives it home.
Ending 2, when you push away Magaleta. Senia becomes consumed by the Eternity, and Magaleta tearfully apologizes to Senia for being a horrible sister while Senia silently and relentlessly attacks her. The image at the end where Senia is collapsed next to the bloody but smiling corpse of Magaleta is the worst part of that ending.
Ending 3, when you do nothing to Magaleta. Magaleta heals Senia by transferring the Eternity from Senia into herself, and teleports her away while Senia insists that it can't be like this. Senia is reducing to slamming her fist against the door and crying while Magaleta calmly tells Senia that she loves her. The music and narration add to this, especially the last line.
