Harry develops the animus after reading about genetic memory and thinking it might be magic and not genetics. His parents are alive in this, Remus is dead as he was babysitting. It takes six years but finally he spends a month in it. He defeats voldemort due to superior knowledge but loses his mind, lost in the bears their child.
James and lily suggest in epilogue she "molest" her comatose husband since they know they planned to have more than one.

Epilogue two has oldest use the chair to find the answer to save Harry. He awakes to find he has a 15yo, an 11yo, and a 6yo. He laughs for hours after hermione tells him she raped him to make the second and third. "Rape me again!"

I started this story already, ignoring the parents alive but but adding in Sirius being free, the two living at Hogwarts. The start of it is in Harry Potter Drabbles. I really love the idea of being able to examine your history that the Animus provides in Assassin's Creed but the ending of 3 crushed me.