Magnus wanted to make amends with Ran. After finding the Summer Sword, Jack, Ran was pissed off with the son of Frey. And when Magnus asked how to be even with the goddess, she told him to find her demigod child, who was as well an einherjar. Here is when Percy Jackson enters. Magnus asked him to help him find the kid, since the son of Poseidon had a connection with the sea, and that kid as well. You were that kid.

Percy and Annabeth joined Magnus, Alex and Samirah in their quest to find you and take you back to Hotel Valhalla.