Zuko tells himself that this is the girl who used to be his best friend.
There are streaks of gray in her hair now, and there are crinkles around her eyes and mouth that weren't there the last time Zuko saw Katara. She is technically still young; none of her children are fully grown. Her body is still curvy and healthy.
It is her eyes that give her away. It is not that they don't shine. They do. It is that there is no longer anything behind the shine. Just two deep blue circles that no longer lead to anything.
Her eyes, Zuko realizes, are void.
"It's been awhile," Zuko says. He smiles at her. He doesn't know what else to do.
Katara turns her gaze to him and suddenly Zuko wishes that she and her husband hadn't come to visit him after all. He didn't think he'd ever see the day where she'd give him such a forced, fake look.
"I've been on the Island," she admits. She doesn't go into further detail, and perhaps that is for the best.
"As long as you're happy." The Fire Lord pulls her into a one armed embrace.
She makes a noncommittal noise in her throat, eyes fluttering, lips curving neither up nor down. The spirited, hopeful girl that Katara used to be not so long ago has not been buried beneath adulthood, worry, and loneliness.
While the Avatar and his friends have built up a new world of peace and prosperity, mounting new cities and bringing bloodbenders to justice, Katara has allowed herself to be left behind.
No, that spirited, hopeful girl has faded away into nothing.
The woman standing beside Zuko is now just a stranger.