Hummingbird [TomRiddlexHarryPotter]

After months of secretly sharing his dreams with Tom Riddle, things take a sharp left turn at the Battle of Hogwarts and when Harry dies and visits the 'train station,' he leaves with an unexpected gift he would give anything to protect. That gift, however, turns friend into foe and forces Harry to flee for his life. But when Harry reaches the end of his rope, he stumbles through a gateway into another world with subjugating Fae Empires, dangerous magical races, and a man sharing the face of his greatest enemy who connected two worlds through shared dreams.

[Or tldr:]
Harry shares dreams with a Tom from an alt universe while horcrux hunting and ends up knocked up. So he of course achieves interdimensional travel in order to claim that child support.