A/N: Some things finally clicked in place about Lin's backstory after 3x05 and 3x06. But lol character altering deus ex machina sixteen hour sleeps are you kidding me. Anyway, here be fanfic.
"Mom wasn't too happy with how either of us turned out. When I was sixteen, I left home to explore the world. I sailed
the seas on a pirate ship, joined a traveling circus for a while, and lived in a sandbender commune in a desert. It took me a while, but I finally realized what I was looking for was a family."
— Suyin, 'The Metal Clan'
Prologue
At eight years old, Lin Beifong knew how to change a diaper, could tell which cry called for it, which keening sounds wanted a bottle, or if the little thing just wanted to be held.
It wasn't because Toph was a neglectful mother. Lin would punch anyone in the face if they made even the slightest suggestion of Toph being incapable of raising her daughters. It was because babysitting a fussy child seemed easier than metalbending training with her mother.
Oh, but she wanted to be a great metalbender and live up to her mother's legacy. Before Toph got pregnant with Suyin, they had already started her metalbending training. Sure, there was the Metalbending Academy in a few years, but Lin wasn't dense like her friends. She wasn't like that stupid airhead Tenzin, who was allowed to mindlessly horse around with his siblings all day. She knew how lucky she was, scoring private lessons with the metalbending pioneer herself.
Metalbending was considerably tougher than earthbending; the latter which, to her mother's delight, came easy to her. Metalbending knocked her out. It wasn't a five hour trek in a dark cave whilst blindfolded (The Toph Method, her mother proclaimed), but it wasn't no walk in the park either. Lin could feel the scraps of steel in her bones, in her teeth, as they clanged and grated and it left her weak, reeling.
So when Toph's maternity leave was up, and little Suyin Beifong could crawl, Lin volunteered to take care of her sister full-time.
"But Linny," her mother said. "Don't you miss training with me?"
Lin blushed and shook her head. She loved her little sister, and she loved her mother even more. Her taking charge would mean less anxiety for Toph, would mean not leaving her kids with a complete stranger. But more importantly, it would shield her mother from disappointment at her inability to master metalbending.
Toph went back to the force, while Lin stayed with her little sister during the day. At night, she packed her bag and took the ferry to Air Temple Island where Aunt Katara homeschooled her along with Tenzin (who was still an airhead, but an airhead she was beginning to grow rather fond of, not that she was ever going to admit it). At the crack of dawn, she would kiss Aunt Katara and Uncle Aang goodbye and return home to Toph and Suyin.
To say that little Suyin was a fussy baby would be a massive understatement. She cried all the time, and nothing seemed to please her.
One day, several weeks into their clockwork routine, Suyin had a grand mal tantrum. The baby hurled her bottle across the room with a strength that made Lin feel helpless. She wriggled out of her big sister's arms. And her cries - the sound of it hoarse and pitiful, was nothing like Lin had ever heard before. It vibrated in her bones, almost like grinding metal.
Toph was due home in an hour, and Lin was at her wit's end. She sat down and hugged her knees as she stared at her wailing sister and felt a tightness in her throat, a sting of tears clouding her vision.
"Stop crying mei-mei," her voice broke. "Mother will be home soon."
She watched Suyin's cries tone down to small whimpers. The baby, who seemed to sense her genuine distress, eventually stopped crying altogether and fell asleep. Lin sat there, in Suyin's dark nursery, staring at the little girl, finally peaceful and quiet, and felt an overwhelming sense of dread she could not comprehend. When she closed her eyes, Suyin's scrunched up face, red and blotchy, swam behind her eyelids like a bad dream - a permanent fixture on the ticker tape of her nightmares for years to come.
Toph found her hours later by the doorway, her overnight bag slung on one shoulder. Tear streaks long gone, breathing finally controlled and less erratic.
"The little badger's out?" Her mother ruffled her hair and she subconsciously leaned into her touch.
"Like a light," she responds quietly. The great tantrum waved off like fine mist. Never mentioned again.
Her mother chuckled and pulled her in for a tight, bone-crushing hug, and Lin found herself barely fighting off a fresh wave of tears.
"You're a natural, big badger," Toph says, peppering her face with kisses. "I don't know what I'd do without you."
Later, on the ferry ride to Aunt Katara's, she would lean out over the deck, and watch each wave fold into itself. She would think of the seeds of fear little Suyin planted into her heart that night, and all the nights before that; of how her innocent baby sister slowly made her feel, for the first time in her life of rock-solid resolve, like a scared little girl.
The Terra Triads had a new recruit, intelligence sources of the Republic City Police Force reported. Her training officer has been breathing down her neck since two weeks ago when a major jewelry store heist broke out, and their only lead was a green satchel stashed with pearl necklaces. The culprits must have left it in their haste to get away from the scene. It was sloppy. And surely, it must have been the new recruit.
Lin needed to close this case. At twenty-three, she could be the youngest female officer to make detective. It fell neatly into place with her precious time frame. Lin Beifong liked to plan ahead. She had strategies and contingency plans for every career milestone the both of them would reach. Tenzin, that stupid airhead (but yes, he's her stupid airhead and she's rather openly fond of him), would tease her lovingly about it.
"It's the rest of our lives, Lin," he would whisper in her ear while he wrapped his arms around her waist from behind. "Not guerrilla warfare."
Lin and Tenzin had it all planned out. If only she could close this one case. And keep her sister Suyin under control.
At sixteen, Suyin Beifong was the archetypal teenage rebel. It drove Lin mad. But at best, it only amused Toph.
"She's spreading her wings! A little rebellion is expected - healthy, even."
"This one though," Toph would wave at Lin's general direction during monthly dinners with Tenzin's family. "This one was born twenty-five. Thank the spirits!"
Lin swallowed back the hurt every time her mother made light of her seriousness. Her iron-clad resolve that she single-handedly forged from what little authority Toph exercised over the sisters. She didn't appreciate being the punchline. Tight pants Lin cleaning up Suyin's mess while Chief Toph Beifong delivered justice to Republic City's outlaws.
But she still loved her little sister. She loved her mother even more. Reprimanding Suyin was a small price to pay because the thought of Su and their mother at odds with each other made Lin feel sick to her stomach. The thought of Suyin's lifeless mangled body in one of the desolate alleys of the city late at night like the cases assigned to her at work made her feel sick to her stomach.
"You're not my mother," Suyin hissed at her. It was the third consecutive night that she sneaked into their house after her curfew with the faint smell of alcohol in her breath. Toph was away for a week-long conference at Ba Sing Se, leaving Lin in charge once again.
A glass of water in one hand, Lin started to lecture Suyin about the dangers of this terrible city at night. Suyin swats Lin's outstretched arm, sending the glass to shatter across the floor. In the darkness of Suyin's room, her glare had a palpable light of resentment directed at her sister. For a moment, echoes of little Suyin's pitiful cries that lonely night years ago flashed into Lin's mind, and then she was eight years old again, crippled by fear, powerless against this small, equally helpless creature.
"You know what," Lin spat back. "I wish I never had to stand up and be responsible for you! I'm relieved that I'm not your mother!"
Tears quickly gathered in Suyin's eyes. And what she said next might as well been a slap to the face.
"Well screw you, Lin. You'd be a horrible mother!"
Lin would not cry. Not when her sister slammed the door in her face. Not when she lingered outside Su's bedroom and listened to her muffled sobs. Not when she walked across the city in the middle of the night to Tenzin's apartment.
Later, sharing the airbender's bed, tangled limbs and sheets and all, she would cry into his shoulder, the solidity of him under her fingertips, and the nebulous, but cherished plans the two of them weaved together easing the sting of her little Suyin's accusations.
"You're not her mother," Tenzin said. "But she's lucky to have you."