Dragon Out of Time: Alduin's Misadventures in a DxD World

Alduin, banished from his homeland by his father, is reborn in the world of DxD, with his soul and power fully intact. However, there's a problem: Alduin is reincarnated not as a dragon, but as a mortal - and not just any mortal, but the younger brother of the future head of Kuoh Academy perverts trio. How will the oldest and strongest of dragons react to this changed world, and how will the world respond to the appearance of a creature capable of consuming an entire dimension? It is based on the existing fanfic called "Братишка" that was unfortunately dropped by its author almost a decade ago (in late 2016).