Another option if they want to stay with the Four Element vers and do a sequel would be to show us what Aang, Zuko and Tenzin did in your body while you were gone.
Like while you power up in their bodies, they lay the groundwork for you to accomplish whatever bulshit the spirit wanted you to and you come home to a harem you don't know much about, just like they do.
And then you do a third game where the MC actualy deal with the spirit bulshit.
It would not be hard to continue that vers while still shaking off any 'project rust' from four element trainer.
This would give you a canon path on the first game...
Since while Aang was pretty much the same in books 1 and 3, despite his relationship with characters being different, book 2 slave route and book 4 love route don't use a canon character for you
Meaning you would be stuck in love route for book 2 and slave route for 4.
I think it would be safer to go what Korra's mom said, that she appeared in MC's body mid-masturbation. Meaning whoever was there before then - and it was not you - was just stuck at home watching porn, probably on the internet.
Probably taken as some Avatar thing by outsiders (which based on what he says can be guesses as having a "finally" somewhere), and took much less time for those in the body than for the spirit/story due to Zuko's leaving ending taking some time.