Altoshipping
Ash, had won, he had won the Alolan League, but he wasn't feeling all that satisfied, leaving him to depart from Alola to go back to Kanto.
Once he got here, he still wasn't feeling all that satisfied, he was longing for something, he just couldn't diagnose what he was looking for. He then realized that it was Latias he longed for, thinking about her made him feel... something that he had never felt before.
He then booked a ticket to Altomare and off he went.
In the secret garden of Altomare, Latias always loved Ash and now he was gone, she felt empty, she was happy that Ash had won the Alolan league. Deep into her thoughts, the phone rang. Bianca picked up the phone and Ash was on the ferry to Altomare, as the call had ended, Bianca told her to wait until this evening.
Time quickly passed and as Bianca and Lorenzo entered the port at evening with Latias behind her who was in human disguise. Latias then met those eyes, the very eyes she got attached to, Ash's eyes, she then telepathized in joy to Ash who was very happy to see Bianca, Lorenzo and Latias.
As they were at the secret garden, Latias turned off her human disguise as Ash was happy to see her. As the sun set below the horizon, Ash made his confessions
"The reason I came back to Altomare was because of you, ever since I left Altomare, a piece of me was empty, I never realized until after I won the Alolan League that I was in love with you, I love you Latias and the barrier between human and pokemon will never make me love you less."
Latias then telepathized in joy as she kissed Ash, right on the lips.
Ash then retired his battling career and settled in Altomare where they became a happy couple