Dobby uses Forbidden Elf magic To Transfer Harry Soul
Dobby survived But Hermione didn't.
After the battle for Hogwarts Dobby notices how the great Harry Potter is In utter agony that miss hermoine died.
Years go by and Harry Potter was never the same after Hermione died. He became Dark And uncaring to anyone other than Dobby and Teddy.
And he was out of control drinking, He went on a couple of months long hunt and ruthlessly Killed everyone who had a Dark mark no matter who they were.
He never spoke to the Weasley family again after Ron and Ginny made horrendous comments about Hermione.
Harry revealed to Dobby one day that he had been in love with Hermione since she was petrified But thought she would never feel the same and that he wasn't good enough for Her.
Dobby is devastated that Harry Potter has lost all the joy in his life and has become a shell of his former self.
Dobby uses Forbidden Elf magic To Transfer Harry potter's soul to his 10 Year old self, He dies in the process.
(No Snape and Draco Redemption)