Promise Beneath the Demon Island
Kai woke before sunrise, the faint gray of dawn filtering through the wooden shutters of the safe house. The air carried the scent of steel and dew, sharp and clean, mingling with the distant sound of blades cutting through wind. He stepped outside quietly and found Toki already practicing.
Her sword moved in smooth arcs, each swing precise and controlled. Hiyori and Kawamatsu stood nearby, watching with wide eyes as Toki infused her blade with Ryo-level Armament, the invisible flow of Haki extending beyond the steel itself.
Kai leaned against the doorway and crossed his arms. "Your control is cleaner," he commented. "Less waste."
Toki didn't stop moving. "It's easier with the Vampire fruit enhancing my senses," she replied calmly. "My Observation reaches farther now."
Kawamatsu blinked in awe. "Lady Toki… you feel different."
Hiyori nodded eagerly. "Aunty is very strong!"
Kai stepped forward, stretching his arms lazily. "We will be leaving in a few days. I have some work to do."
Toki lowered her blade and looked at him. "Onigashima?"
Kai's lips curved faintly beneath his maskless face. "Yeah."
She nodded and turned to Hiyori and Kawamatsu, explaining briefly that Kai would be gone for a short time. Kawamatsu listened carefully, while Hiyori looked a little worried but tried to smile bravely.
"Brother Kai always comes back," she said confidently.
Kai ruffled her hair gently. "Of course."
---
Later that morning, Kai fastened his Oni mask over his face. His wings unfurled in a smooth motion, feathers catching the rising sunlight as he leapt into the air.
He flew toward Onigashima, the massive skull-shaped island looming over the sea like a sleeping beast. As he approached, he shrank his body mid-flight, reducing his presence and aura.
He circled behind the island, gliding toward the forest and cliffs hidden from the main stronghold. Once deep enough into the shadows, he returned to his original size and hovered lightly above the ground.
A sudden white blur shot toward him.
Before he could react, it slammed straight into his chest.
Both of them crashed onto the forest floor, leaves and dust scattering around them. Kai let out a soft laugh instead of resisting.
Yamato clung to him tightly, her white hair falling around them like snow. "You came!" she exclaimed.
Kai chuckled, arms wrapping around her waist as they lay tangled on the ground. "Your Observation has grown quite strong," he teased.
"Of course it has!" Yamato replied proudly. "I have been training hard. I can already use Armament Hardening. And I can activate Conqueror's when I want."
Kai smiled warmly. "Well, Yamato is the best after all."
She giggled, her horns brushing lightly against his shoulder as they shifted under the shade of the trees. The forest was calm, insects humming softly while sunlight filtered through the leaves.
They lay there quietly, snuggling beneath the canopy. Yamato rested her head against Kai's chest, listening to his heartbeat, while his arms wrapped around her neck and waist protectively.
"Don't leave so quickly next time," she murmured sleepily.
"Then stop hugging me like a cannonball," Kai replied with a soft laugh.
They both drifted into a peaceful nap, their breathing syncing in the stillness of the forest.
---
After a few hours, Yamato woke first. She didn't move, simply staring at Kai's face while he slept, mask removed and expression calm.
"You look younger when you're not smirking," she whispered softly.
A few minutes later, Kai's eyes opened slowly. He blinked once before smirking. "You're staring."
Yamato jumped slightly. "I wasn't!"
"Liar," he said lightly, sitting up.
Kai stood and walked toward the edge of the forest. He had hidden something there earlier, anticipating Yamato's explosive greeting.
He returned carrying a wrapped bundle.
Yamato tilted her head curiously. "What's that?"
"Gifts," Kai replied casually. "I left them far away because I didn't want them crushed by your wild hug."
Yamato pouted. "I'm not that wild!"
"You tackled me from the sky," Kai deadpanned.
She laughed as she opened the bundle. Inside were carefully prepared foods—dried meats infused with spices, preserved fruits, sweet rice cakes wrapped tightly to last longer, and even rare imported candies.
Her eyes sparkled immediately. "You made these?"
"Had them specially prepared," Kai corrected. "Food that lasts longer. Easy to hide."
Yamato didn't wait for further explanation. She began eating with pure delight, her expression blissful.
"This is amazing!" she said between bites. "Better than what we get inside."
Kai sat across from her, watching quietly. "Eat slowly," he warned. "You'll choke."
"I won't," she insisted, cheeks puffed.
After eating, Yamato jumped to her feet, energy returning instantly. "Let's fight!"
Kai stood up calmly. "Show me."
Yamato's arm darkened with Armament Hardening as she swung her kanabo downward. "Thunder Bagua!"
Kai stepped aside smoothly. "Too straightforward."
She pivoted mid-swing, bringing the club around horizontally. "I'm not done!"
Kai blocked with his forearm coated in Armament. The impact cracked the ground beneath them.
"Better," he said. "But you're still relying on brute force."
"I am Kaido's daughter!" she retorted fiercely.
"And you don't have to fight like him," Kai countered.
Kai nodded approvingly. " Don't release armament everywhere. Focus it."
She narrowed her eyes and concentrated, compressing her will into her Kanabo.
Kai continued. "Infuse it with armament."
Her kanabo turned faintly black. She lunged forward again.
Kai met her strike with his own Armament. The clash split the air with a sharp boom, sending birds scattering from the trees.
"Feel that difference?" he asked mid-combat.
Yamato grinned fiercely. "Yeah! It's stronger!"
"Control it," he instructed as he parried her next blow. "Don't let it leak."
They exchanged several more blows, each heavier than the last. Yamato adapted quickly, adjusting her stance and timing.
She swung low, then feinted high. Kai raised a brow.
"Nice feint," he acknowledged.
"You noticed?" she teased.
"I always notice."
Eventually, Kai stepped back, lowering his guard. "That's enough."
Yamato panted lightly but looked proud. "I've gotten stronger, right?"
"Yes," he answered honestly. "Much stronger."
Her bright smile slowly faded as she realized he would be leaving again.
Kai noticed immediately. He sighed softly and stepped closer, pulling her into his arms.
Their foreheads touched gently.
"Hey," he whispered.
"Hmm."
"Don't worry. Very soon, I will take you to the sea. We will travel and eat many different foods."
Yamato's grip tightened slightly. "Hmmm… promise?"
"Yap," he replied firmly. "Promise."
She finally smiled again, though her eyes were a little watery. "I'll get even stronger before that."
"I know you will."
They stayed like that for a while longer, holding onto the moment. Eventually, with visible reluctance, Kai pulled away.
"I have work to finish," he said quietly.
"Don't die," Yamato replied.
"Not planning to."
He stepped back, spreading his wings once more. Yamato watched him rise into the sky, her expression determined.
---
Kai flew back toward Wano, mind calculating.
He was nearly ten years old now. Four years remained before the Giant King would lose control under Imu's Sea Contract.
His next takeover target.
If he could secure Giant King Harald at that moment, everything would change. With the giants power , his power would skyrocket.
He wouldn't have to leave Yamato behind anymore.
Kai's eyes burned with quiet resolve beneath his Oni mask.
"Four years," he murmured to the wind. "That's enough."
His resolve burned harder and brighter as he disappeared into the horizon, already planning the storm that would shake Elbaf itself.