Harry Potter and the Simplest Solution part I (гет)

Harry boards the Hogwarts Express for his first year at Hogwarts, but everything is not what it seems. Harry has come back from the future to defeat Voldemort, but he only has a few hours in which to do it. He needs to find the simplest solution...
A unique and fast-moving Harmony "redo" like nothing you've ever seen before.
The Harmony stuff takes off in part III. That's where the feels begin... :)
Some genuine reader comments about this series:
"In ten years of reading HP fanfics I don't think I've read such an original and moving story."
"This has got to be one of the most beautiful, organic and satisfying Harmony fics on AO3."
"I'm just gonna call this series, 'How [the Harry Potter Books] Should Have Ended'."
"You've turned me into a crying mess! Thank you for such a beautiful story!"
"I've reread this series over ten times but I still can't stop the feels."
"Gave me chills! Even now I still have goosebumps!"
"Heart-wrenchingly beautiful."