I honestly came here expecting it to be more like "How did it end for you?"
Spoiler: After the last gym, a mysterious storm is found in Route 7. This is actually irrelevant to the main story, but it's worth mentioning. Anyways, you go through Victory Road like normal, and then come to the Elite 4. Beat them, like normal, but in whatever order you choose. When you finally get to fight Champion Alder, you find N beat you to it. N's castle rises out of the ground and overtakes the mountain that is Victory Road. As you enter, you're confronted by six of the seven sages of Team Plasma. All gym leaders except the first come to aid you by stopping the sages and allowing you to continue. You have to explore the castle to find N. After you find him, you fight him (obviously). You're required to capture and use Reshiram against him, however. After defeating N, Ghetsis appears and challenges you. Ghetsis reveals that he was just manipulating N to attain his own goals of ruling the world. Ghetsis is arrested upon defeat, N realizes he was just a pawn, and the game ends here.
click to reveal
There's much more to the game, but it's not required, and is too much to type.
The one and only!