I’m Invincible with a Game System

On the day Ying came of age, she secretly made the same wish she'd repeated for eighteen years: If there really are gods, please let me transmigrate into an anime and go on adventures with the characters I love! Then Game System 12138 appeared. "Your wish has been granted. Game System 12138 is at your service! Choose a world, and you'll have access to every game you've played. You can choose only one game per world~"

Jujutsu Kaisen: Jujutsu Resonance

When Satoru Gojo was 27, he killed his best friend with his own hands. But when he was 28, he saw his 17-year-old best friend shopping with a long-haired girl, the two of them acting very close.

Satoru Gojo: pupils trembling (the daifuku in his hand drops to the ground)

Megumi Fushiguro had grown up alone from a very young age. He never thought he wanted a happy childhood, until he saw on the street a figure who looked like his awful dad, carrying a six-year-old child who looked a lot like him and walking alongside a girl. They looked like a happy family. Only after their backs disappeared from view did he realize he had been crying without noticing.

Le Kuan?

Theme: Save the characters who never got their happy ending