Since playing and finishing Sun, I’ve come up with a ton of headcanons (several with @8bittheatrics help) and I felt the need to share them. They’re primarily based on my own character and as such I’ll be using he/him pronouns when referring to the MC, but they should fit with any version of the MC if you want them to.

• In the future, the main trio has become some of the most prominent figures in the Alola region
• Hau is the Kahuna of Melemele island taking his grandfather’s place and is widely known as the strongest of the four. He’s beloved by everyone across the region because of his sunny personality and love of everyone he meets.
• Lillie, after travelling to the other regions and studying with the other professors, returns to Alola and takes Kukui’s place as the regional professor. Inspired by professor Oak and her own experiences with Nebby, she studies the relationships between people and Pokemon
• Sun is still the champion even years later and is one of the longest-reigning champions in the world. Known across the region for his endless faith and love for his Pokemon, he’s an inspiration to young trainers everywhere starting their journeys.
• Whenever there’s a new trainer coming to get their first partner from Hau, Sun and Lillie always come in order to give their advice and well wishes as well as formally explain the island challenge.
• Sun and Lillie are predictably married and have a daughter (still thinking of a name for her. I’m open to suggestions). She’s crazy about Pokemon. Like, Pokemon are her everything. Her parents are very proud.
• She’s best friends with all of her parents Pokemon, but she’s especially close to Sun’s starter and Nebby.
• Also because of Sun assembling all of the Zygarde cells and cores together during his first journey, it spends most of it’s time at their house in it’s 10% form. The daughter calls it Squishy because of it’s core form.
• Once their daughter goes on her journey and Sun is away because of champion duties, Squishy spends most of it’s time with Lillie in the lab. One day, a foreign professor visits and is just kind of baffled by the fact that Zygarde is napping in the corner
• Lillie: 

  “Zygarde? Oh, you mean Squishy, yeah it usually keeps an eye on my daughter, but since she left her journey and my husband doing champion things, it just naps here in the lab”

• Professor: “It seems a little lonely”
• Lillie: “Oh, no worries. It can replicate itself, it has five cores in there after all. If you’re lucky, maybe you’ll get to see it. 

  Though it gets to be a hassle when it replicates itself into five. It may be the Order Pokemon, but it’s extremely good at making a mess, yes I’m talking about you and how you tracked mud all over the house yesterday"

I have more headcanons, but they involve spoilers from the game.