Zuko’s favorite time of day is bath time.
He loves the way the water feels, soft and comforting and right in a way he doesn’t quite know how to explain. He loves being allowed to splash and play and laugh as he watches the tiny waves he can make just by pushing his arms through the water.
(He doesn’t notice the way the waves are just a touch larger than they should be, the way the ripples he causes last just that bit longer than they should. To Zuko, it’s just the way water works.)
He kicks and splashes and laughs at the way his hair floats and moves along with the little waves in his bathtub, and thinks, What would it look like if all my hair was in the water?
The first time he tries putting his head underwater to see, Mom pulls him out of the tub before he even has a chance to look. Mom tells him bath time is over and ignores his whining as she wraps him in a towel and carries him back to his room. She doesn’t let him go back to the bath, but she pulls out Love Amongst the Dragons to read, and Zuko temporarily forgets about the bath in favor of listening to his favorite play.
During his next bath time he’s distracted by the fact that he’s sharing the bath with a turtle-duck. It’s not real turtle-duck of course, but it floats like one and if he can move just right he can use the little waves he makes to make it float around the tub like it’s swimming. And then he accidentally discovers that it makes the best noises when he squishes it, which makes it almost as good as a real turtle-duck. Maybe even better, because he’s not allowed to play with the real turtle-ducks.
(Zuko never notices his mother swearing his bath attendants to secrecy, because even a hint of a whisper that Zuko can water bend reaching Ozai’s ears would be disastrous. Once Zuko asks her why Azula doesn’t have baths at the same time as him, and Ursa gently explains that his sister is still too little to have as much water in the baths as he likes to play with. Zuko accepts that he’ll have to wait until Azula is bigger to show her how awesome bath time is, and Ursa is relieved that she can wait a little longer to tell her son that the reason he’s yet to throw sparks is that he was born to bend a different element.)
The toy turtle-duck is fun to play with, but his favorite part of bath time is still the water. He gets distracted watching the waves and ripples, and then he’s wondering again what his hair would look like all in the water. So he leans forward to find out. He realizes almost immediately that he’s made a mistake—the ends of his hair were floating earlier, and that didn’t change when he stuck the rest of his head in—which means that he’s looking down at the bottom of the tub instead of at his hair. His Mom pulls him out of the tub a moment later, and he doesn’t get the chance to try again because every time he tries to lean his head back into the water Mom stops him before he can even get his mouth under the water.
(Meanwhile Ursa is trying to explain to her child that he needs to stop doing this because even water benders can’t breathe underwater. Zuko’s exclamations about wanting to see his hair only manage to confuse her—what does his hair have to do with breathing?—but she recognizes that Zuko is determined and increases her vigilance accordingly.)
He’s frustrated that Mom keeps stopping him from finding out what his hair look like underwater, but eventually he realizes that Mom isn’t going to change her mind.
This does not mean that he’s given up. He knows Mom won’t let him put his head under the water, so he has to try it when Mom isn’t paying attention.
…He’s not very good at figuring out when she isn’t paying attention. He never quite manages to get all the way under the water before she stops him.
(Zuko fails to realize that this is because Ursa is always paying attention to Zuko, especially when he’s around significant amounts of water, and even more so now that she’s discovered her child’s apparent fascination with being underwater.)
Then one day Mom has to leave in the middle of bath time. He doesn’t quite catch what the palace messenger who called her says because they’re talking too fast and loud and the words get all mixed up as they bounce around the room. But Mom leaves with the messenger. He keeps playing for a little, but when Mom doesn’t come back right away, he decides now is his chance. He lays down on his back and watches with amazement as his hair rises up toward the surface of the water, swaying back and forth in the waves he made when he laid down.
He starts feeling an itchy sensation but ignores it in favor of watching his happy sigh form a trail of bubbles up to the surface. The next second his vision goes blurry and his entire body shudders like Azula dropped something gross down his shirt and suddenly he’s floating instead of under the water and the tub looks much bigger than it did a moment ago.
He tries to sit up but flails instead because his limbs aren’t moving the way he expects them to, and ends up floating on his stomach. He blinks in confusion. His eyes are still above the water, but his neck doesn’t feel weird at all from the way it has to move for that to happen. After a bit of trial and error he manages to wiggle towards the edge of the suddenly-large tub—
—and screeches in surprise when he sees a dragon instead of his reflection. Several minutes of confused flailing later, he figures out how to twist the right direction to actually see himself and yes, he’s definitely red, and much skinnier and smaller than he remembers being, and his legs are shaped weird with fins on the ends instead of toes.
He somehow managed to turn into a dragon.
He’s also now the perfect size to pretend to be a sea monster and chase the toy turtle-duck around.
This is awesome.
(Ursa returns to find the bath attendants in hysterics and it takes at least ten minutes to calm them down enough that they can speak in coherent sentences, at which point they tell her that they only looked away from Zuko for half a minute at most and when they looked back the Spirits had replaced him with a dragon. They were too afraid to go near the tub, but they searched the whole room and couldn’t find Zuko, what other explanation could there be? Ursa takes one look at the tiny dragon—it can’t be any longer than her arm—trilling as it chases her son’s toy turtle-duck around the tub and knows—)
He clumsily skids to a stop and raises his head to look around, blinking in shock at how much bigger Mom looks.
“Is that you, my son?”
He nods his head yes, and has to flail his limbs a bit to keep floating in place because he forgot how long his neck was.
“How did this happen?” Mom asks.
He hasn’t figured out how to talk as a dragon yet, and even if he had he doesn’t know why he turned into a dragon, so he just looks back at her and chirrs.
“Oh dear,” she murmurs. “Well, dragon or not, you need to come out of the tub and dry off.”
Mom extends her arm to pick him up and he huffs and sinks deeper into the water in protest. He was having fun! She reaches into the water and he’s still too clumsy to dodge her hand for long, so he gets grabbed despite his best efforts to stay in the water.
Since he can’t complain in words, he expresses his displeasure by drooping limply in her hand so that his limbs trail in the water as she pulls him out of the tub. Being dried off with towels feels very strange, and he hisses in protest at the sensation and tries to wiggle away, but the towel is too big for him to escape. He still feels a bit damp when he’s freed from the treatment, sort of like when his hair takes a while to dry. Twisting to examine himself, he realizes that instead of scales he’s covered in very short red fur.
It puffs out slightly when he feels himself picked up without warning, but he’s distracted from his surprise by the sensation of warmth and he happily curls around it. Now comfortably warm, he’s asleep in moments.
(Ursa sends prayers of thanks to every Spirit she knows that Zuko returns to human form after a few agonizing hours, and starts making plans. If they’re lucky, her husband will never discover this strange new ability of Zuko’s. But Ursa has never been willing to rely on luck.)