A short headcanon featuring a handful of the JJK cast in Pacific Rim Universe.
Ryoumen Sukuna/Itadori Yuuji.
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When Sukuna and his twin brother joined the Yeager Program, the two drifted together - seeing as they were siblings. But then Yuuji, after starting a relationship with the ever stoic Chouso Kamo - a distant cousin of theirs - stopped drifting with Sukuna and started piloting another Yeager with Chouso.
The organisation was hesitant about it at first, but when they saw how compatible Yuuji and Chouso were, they let one of their star users be.
Thankfully, and unfortunately in Sukuna's perspective, the taller of the Itadori twins was compatible with a Yeager fighter by the name of Uraume. If Sukuna wasn't so nonchalant about his dog like attitude with him, Sukuna would be kind of irritated about his ass kissing.
The issue of the Yeager partner changes made the two Itadoris have a huge fight that saw them, well more like Sukuna, not talking to each other or meeting eye to eye. His dismissal of Yuuji had the smaller twin feeling dejected and not knowing what to do to fix their crumbling relationship.
Worse of all was that he didn't get along with Chouso, who was to soon be his brother in law. Chouso, who was close to both of them from childhood, was now seen as an enemy by Sukuna and the older twin didn't hesitate in making his annoyance known whenever Chouso arrived.
Sukuna ignored their very existence, even during briefing hours. Yuuji, as well as others, tried to reach out to him, but like the expert he was, he shut them all out.
When Chouso died during a battle against a Kaiju in the sea, Sukuna had never felt so much GLEE until that day. But that glee turned soured when the organisation didn't give up Yuuji's location. They said that his brother wanted to stay off the grid and away from Yeager business from then on.
Oh, Sukuna looked for him on his own of course, but it seemed that Yuuji knew how to hide himself well from the rest of the world when needs arises.
It wasn't until four years later that Yuuji came out of hiding, due to the organisation's coaxing. Sukuna had to blink in surprise at the scars in his face which changed his appearance quite a bit.
Yuuji gave his brother a shy smile, which had Sukuna rolling his eyes and pulling him into a hug. Yuuji buried his face into Sukuna's chest, inhaling the familiar scent of his brother.
With him feeling at home, at last, in Sukuna's arms, the shorter pinket wondered what caused them to drift apart those years ago, and he couldn't come up with a solid answer in his mind.
Problem arose when the organisation looked for who could drift with Yuuji in the repaired Yeager. Sukuna asked - more like ordered - that he and his brother should be on the same team once again.
Of course the organisation, and Yuuji, made mention of Uraume being his partner already, but Sukuna shot them down, saying that Uraume understood and cared not about being benched for the time being.
They looked at said person in question and they affirmated to Sukuna's statement with a stoic face.
And so, the Itadoris became one again. Of course trouble arose with Yuuji still having problems letting go of Chouso and the memories of that night in the sea still haunting him. His rampant memories almost saw their Yeager blowing up the base with a plasma cannon.
The Commander of course was pissed, but Sukuna stepped up and protected Yuuji. Sukuna's fierceness for shielding his brother had Yuuji's heart skipping a beat and a heavy blush to dust his cheeks.
The two were put on hold and they used that moment to try to patch things up.
Yuuji asked what exactly had he done to wrong his brother that caused Sukuna to ignore him all those years ago. Yuuji also asked why did the tall behemoth had an issue when he brought Chouso as his boyfriend turned fiancé, but Sukuna didn't answer.
The answer would have to wait, seeing as Kaijus had been sighted. They wanted to join the fight but were denied. They weren't put on the field until one of the Kaiju caused an EMP surge, and luckily, their Yeager was analog and ran on nuclear power of its own.
When they drifted, Yuuji had to overcome his grief and guilt for the betterment of the mission. The two drifted successfully, but not until Yuuji caught sight of a glimpse of an interesting memory from Sukuna.
As expected, they kicked the Kaijus asses, grinning in exhilaration and bloodthirst all the way.
A way was soon discovered to close the Rift once and for all, and the twins agreed in following the Commander to the bottom of the ocean.
Said commander was accompanied by Toji Fushigoro to pilot the only other nuclear run Yeager.
Toji and his son were the ones Sukuna and Yuuji rescued the very last minute. They too had the same bound like the Itadori twins and were perfectly compatible. Unfortunately, Megumi was injured, so Toji took the chance to help his old friend once more. Toji pulled his son into one last deep kiss, which the teen sobbed against, before pulling away and following after the commander to suit up.
The two teams made it to the bottom of the Pacific ocean. They fell into a trap and Toji and the Commander had to activate the bomb to make a way for the twins to finish the job.
With their broken Yeager and a Kaiju corpse in hand, the two successful passed the Rift.
Due to lack of oxygen and exhaustion, Yuuji was teething into unconsciousness. Sukuna activated Yuuji's escape pod and sent him up whilst he activated the nuclear bomb by hand. He almost got himself killed by almost slipping into the large fan, but he succeeded in getting to the switch and activating the bomb sequence. He made it to his pod and escaped.
The blast from the bomb had his pod propelled up and faster, and he narrowly escaped from the closing Rift.
Yuuji, who was back to himself, waited for the arrival of Sukuna's pod. When it came to the surface, the pinket heaved a sigh of relief, but then got so worried when the pod didn't open.
Something was wrong. Sukuna should have opened his pod already.
Yuuji jumped into the water and swam over to the pod. He got on top of it and opened it with the emergency latch. He looked at Sukuna's still face in worry, terrified to the core when he realized that his brother wasn't breathing.
He did some chest compressions on Sukuna, lightly slapping his brother's face. Sukuna didn't respond and Yuuji thought the worst.
With a sob, he grabbed Sukuna and pulled the unmoving man into a hug.
Yuuji had never been glad to hear a cough so much in his life until that day. Sukuna joked in his ear with a raspy voice about Yuuji trying to choke him and the pinket let go of his brother in shock.
With tears in his eyes, Yuuji grabbed his brother's face and pulled his Sukuna into a deep kiss, shocking the older twin.
"Wow." Sukuna breathed out, blinking at Yuuji with shock.
"I saw your memories, Nii-san. Your confession to Uraume san." Yuuji said shyly. "You're not the only one who feels the same way."
"Huh. So I could have gotten a confession from you if I pretended to be dying in your presence all those years ago, huh?" Sukuna grinned at Yuuji, who rolled his eyes in exasperation.
"Don't push it, Nii-san."
Sukuna let out a deep chuckle before gently grabbing Yuuji's face and pulling him into a chaste kiss.
Yuuji closed his eyes and deepened it and the two made out right there in the ocean, not caring about the passing aircrafts or that the whole control room in HQ could hear them.
Seeing as the Kaiju menace was over, the two retired, going to live a quiet life in a secluded area in the mountains, surrounded by nature.
Their first night consummating their relationship was soft and gentle. Sukuna handled Yuuji with care, showering the man with attention, love and pleasure. He had Yuuji moaning and mewling his name, opening up beautifully for his Nii-san, and taking what Sukuna gave him with happiness.
There wasn't a day that the two didn't head for the cliff close to their home and sat down at the edge of it, with Yuuji leaning on Sukuna and his head on his brother's broad shoulder as the two stared out into the horizon.