Mob Shoujo ga Last Boss Majo wo Shiawase ni Suru made

"I want to see your smile again" — A new girls' fantasy! A girl remembers. That this is a game world. That she had been reincarnated as a mob character. That her best friend would one day become a witch who freezes the world. And — that she would become the final boss and be destroyed. "I promise, I won't let Grace become a bad person." She refuses to accept such an ending! The girl Roselika makes her resolve and takes the hand of her best friend Grace, who has manifested the supernatural power that will turn her into a witch. She pulls her away from the family that drove her to the edge, and uses every bit of knowledge she has to defy fate. Gradually, Grace's frozen heart begins to thaw — "No matter what happens, I won't have any regrets. Because I love you, Roselika." — Being told that so directly... my heart can't help but race.

(Source: Fantasia Bunko, translated)