Headcanon/fic-cy thing:

A-Yuan still has the butterfly 16 years later because lwj made sure he would, determined that A-Yuan would keep hold of everything from that one beautiful day they got to spend together. Determined that A-Yuan would know all the ways his father loved him

He emulated the ways wwx loved A-Yuan at first, which was...difficult, though not as much as he thought it would be. His mother aside, his family had never showed open and carefree affection but...wasn't that what he learned from wwx?

So he mimicked wwx's love for A-Yuan until he learned how to show his own – and discovered they weren't very different at all, he'd just never had the chance to try

Because of his illness A-Yuan remembered nothing and, as he grew, would sometimes ask about his family. lwj was honest, always, saying that he didn't know much but that they had loved him just as deeply as lwj did

As A-Yuan became older still and understood more, lwj was finally ready to give more details – that A-Yuan's father's love had been reckless, all-encompassing and that he'd taught lwj to love the same way

That he was the best man lwj had ever known, always trying to protect the weak and defenseless, to do what was right

A-Yuan asked him, once, if lwj had loved him too.

“Very much,” he replied, voice rough, eyes wet, because he had never lied to his son and he wouldn't about this, either. “I will never love another.”

That saddened A-Yuan but lwj assured him that all was well – his love for wwx had been a gift he had never expected or dreamed of getting, and even if he hadn't had A-Yuan, everything he'd suffered would've been worth it for that alone

“Still,” A-Yuan had pouted, “I hope someone makes you happy again someday.”

“You make me happy every day,” lwj promised

“I know, Dad,” A-Yuan grinned, even rolling his eyes a little and it warmed lwj's heart that his son was so certain of his love for him, “but it's not the same. You never know,” he urged, “the world is very large and strange. It could happen.”

“It could,” he said. “Though it seems unlikely.”

“But not impossible,” A-Yuan insisted, gesturing with his hand in a way that was so reminiscent of his father.

“But not impossible,” he conceded with fondness, though he didn't believe it

Less than a decade later, lwj heard a flute playing their song in the woods and he – moved. Ran, flew – without thinking, without breathing, his heart guiding him straight towards the thing he had always known he would never have again.

Straight towards the impossible