extra’s rebirth: i will create a good ending for the heroines

“Everyone deserves a happy ending, don’t they?”
…
In the brutal fantasy RPG Fall of Ares, saving the world came at a cruel price — the deaths of every heroine the player had grown to love. 
No matter how skilled you were, their sacrifices were inevitable. 
The game warned you not to get attached.
But one young man did.
After beating the game and lamenting their tragic fates, he wakes up in its world — reborn as an extra, armed with one mission from a mysterious system:
[Change their endings. Let them live.]
Now enrolled at Astralis Academy alongside the heroines doomed to die, he must rewrite fate itself. 
For every girl he saves, he’s rewarded. 
But the world resists change. 
Calamities draw closer. 
The true enemy — the Children of the Sky — are watching.
And one of the heroines… remembers it all.