Gatekeeper's dual identities are Ka'ahupahau and Kahi'uka, the Shark Siblings of Hawaiian Mythology. However, they were actually born as ordinary humans. The twins' mother, believing the children were stillborn, impulsively hurled them into the depths of the sea. Miraculously instead of dying, a passing shark-god took pity on the babies and transformed them into shark-gods too.
Having known no human warmth in life, Ka'ahupahau quickly embraced the life of a man-eating shark. She killed and terrorized countless humans, becoming hated and cursed by them in turn. Her brother Kahi'uka had a gentler nature, but he felt obliged to protect Ka'ahupahau despite not condoning her actions, as she was the only person he had in the whole world. Until, a day came when everything changed.
Ka'ahupahau came across a young girl named Papio who'd been out surfing one day. The girl came across a shrine of some flower-crowns that'd been offered to Ka'ahupahau in the hope of appeasing her ire. Innocently fascinated by the pretty weaves, Papio tried to take one for herself. Ka'ahupahau was furious at this, and went to kill the girl on the spot. But when she saw the girl's eyes, she hesitated. Papio's gaze was scared, but didn't hold any hatred towards her, unlike the other humans she'd devoured. She just asked her in a wavering but firm voice "Miss scary shark lady, why do you kill humans? Sharks killed my mama and my grandpa too, so I guess I should hate you. But instead I just want to know, why? Do you hate us that much? Did we do anything mean to you in the past?"
Ka'ahupahau was taken aback, having no answer to the girl's innocent questions. Even though she was terrified for her own life Papio hadn't hated her, but instead made a sincere effort to understand. The shark's bloodthirst evaporated, and she ended up talking with the girl instead. Papio about her family, the taste of fruits, and the other kids at her village. She came from a poor village so it was hard to scrap by enough food to survive sometimes, but everyone did their best and pitched in to help each other when they needed it.
Ka'ahupahau marveled at these stories. She'd never known anything about the humans she'd killed, only blaming them for abandoning her at birth. To think that humans could show warmth and kindness to each other made her question everything she knew. In turn Ka'ahupahau told her companion all about what it was like to live in the ocean. The schools of fish swimming by your face, the forests of coral and shells gleaming like gems on the seafloor. Papio was enchanted by everything the shark told her, as she'd always dreamed of living in the sea. "That's so cool Ka'ahupahau. But..." The young girl frowned, a more contemplative look crossing her features. "Can you stop killing humans? I'm glad you haven't hurt me, but I'd feel awful if you ate my dad or anyone else in my village. So please, don't kill anyone else okay?" she pleaded, big brown eyes welling up with tears.
"I promise," Ka'ahupahau said, surprising even herself. For some reason, she just couldn't bring herself to against this girl's purehearted request.
"Yaay!" Papio cheered, her face lighting up in a big smile.
For the next few weeks Papio and Ka'ahupahau often met up and talked, sharing stories of their lives on land and at sea. As humans still hated and feared sharks, Papio had to sneak down to the shore early in the morning to visit her new friend in secret. Ka'ahupahau meanwhile was slowly growing weak from starvation as she wasn't used to abstaining from her usual meal of humans. But she hid her pain from Papio to avoid worrying the other girl.
Then, tragedy struck. One day when Papio was visiting the shore as usual to see Ka'ahupahau she was attacked by an evil shark that just happened to be stalking the area. It'd taken advantage of Ka'ahupahau's weakness to encroach on her usual hunting-grounds. Ka'ahupahau arrived just in time and when she saw the evil shark about to kill Papio, something snapped inside her. She flew into a rage, all the bloodlust and aggression she'd pent up erupting outwards all at once. Ka'ahupahau savagely mauled the evil shark, ripping it to pieces with her teeth. Her mind was painted red, all thoughts drowned out in the sheer instinct to kill. And... when she regained her senses, a horrible sight confronted Ka'ahupahau.
Papio lay skewered on her teeth, the girl's innocent face twisted in a look of pain and confusion. Ka'ahupahau must've accidentally struck her too when she was in a rage and couldn't tell friend from foe. "Ka'ahupahau..." Papio murmured, blood seeping from her mouth. Every syllable was a struggle that felt like needles were stabbing her lungs, but she was determined to get out the last words to her friend. "I... forgive you. I know you were just... trying to protect me..." Her eyes carried no hatred, only longing and sadness. "But please... promise me one last time... that you won't hate humans anymore. That you won't... hate yourself anymore. Because... I believe that someday, humans and sharks will be able to live in peace and help each other. And... you're the one I trust to carry out that future. That's why... I'm not scared..."
The girl's voice faded to a whisper before finally flickering out of the world altogether, before Papio's eyes drifted peacefully closed for the last time. "Paaapppioooo!!!" Ka'ahuphau turned to the skies, howling out in rage and sorrow. For six days straight she wailed and thrashed in the water, mourning the life of the first human she'd ever called a friend. Then finally when Ka'ahupahau's despair dimmed to a dull ache she brought Papio's body gently out to sea, giving her an honorable "burial" beneath the waves. Over the girl's body she swore a solemn oath that'd bind her for all eternity. Never again would Ka'ahupahau stain her maw in the blood of humans. Instead, she would prey on the evil sharks that threatened them. She would protect the humans that feared and scorned her, in honor of the one girl foolish yet kind enough to worm a way into her heart.
Having sworn that oath Ka'ahupahau swam back to rejoin the rest of her pack. She easily talked her brother Kahi'uka into joining her new path, for he was a kind person who disapproved of her slaughter of humans even before. And it wasn't long before other sharks came to follow them, either out of morals or simply sensing more reward to be gained by currying favor with the humans.
As decades passed Ka'ahupahau and her brother came to be revered as divine protectors of mankind, with their vicious origins largely forgotten in the foam of history. But--- she would never forget. The oath she swore on that day, and the last wish of that girl who believed in her more than anything.
For her sake alone--- Ka'ahupahau would always continue to fight.