-Yamamoto's POV-
'I'll have Shunsui start taking over the First Division.' I sighed wearily. A few minutes had passed since Sasaki had left, and now I felt Unohana's presence as she arrived.
"Captain Unohana." I greeted, lifting my head from the documents outlining our strategy against Yhwach. She nodded and stepped closer.
"I'm here for the key to Muken."
I rose and walked to the edge of the ruins. From here, I could see the extensive devastation that remained. "No need." I replied. "I've assigned someone more suitable to handle Captain Kenpachi."
The air stilled, thick with her silence, until she spoke in a low tone. "Who? Other than you, Squad Zero, and myself, I doubt anyone can draw out his full potential."
I returned to my desk and responded calmly. "Sasaki Ryou."
A Hadō shot past my head, and I looked at her from the corner of my eye. "Captain Unohana, mind yourself."
She narrowed her gaze at me as I resumed my seat. "I thought you despised the idea of a human involving themselves in Soul Society's affairs."
"You're correct." I responded, resting my hand on the table as I met her gaze. "I will have Captain Kyōraku take over the First Division, so before that happens I shall make changes to aid him and the Soul Society. This is one of those changes." My eyes narrowing at her. "Tell me, are you concerned about never being able to atone for your sins… or about Sasaki-san?"
She offered no reply and left. I let out a sigh, then turned back to my papers.
-Ryou's POV-
Muken, the lowest level of the Central Great Underground Prison, was vast, seemingly endless. 'Probably some kind of spell.' I thought, glancing around at the stone pillars breaking the darkness with thin beams of eerie light. With a sigh, I opened the cloth to reveal Muramasa, split into two broken halves.
Though it now looked like an ordinary katana, lacking even a hilt, I knew what this sword had endured. 'For all the trouble you've given me, I'm sorry to see you like this.' I thought, gripping the tang as I sensed familiar Reiatsu approaching with heavy footsteps.
"Eh, Ryou?" Zaraki's voice called out. "Thought Unohana was supposed to be here."
I hummed, tucking the broken blade into my obi, and removed my eyepatch, turning to face him. "Kenpachi Zaraki." I declared. "in true Kenpachi tradition, I challenge you."
His eyes widened in surprise, but soon a grin stretched across his face as he rested his sword on his shoulder. "What the hell are you talking about? Cut the crap Ryou, and tell me what's going on."
I tilted the broken form of Muramasa, channeling half my cursed magic into myself and the sword. Grinning, I yelled. "What, you need a reason to fight?!"
Before he could answer, I Shundō directly in front of him. "Twice Over: Cursed Slash!" A purple, black, and red colored sword slash struck across his torso from shoulder to waist, sending him crashing into the stone pillars. 'Gotta keep the pressure on him.' I thought, using another Shundō to close the distance as he began to rise from the rubble.
Seeing his grin, I launched my next attack, this time infusing bloodlust into the strike. "Nemesis Cursed Slash!" The slash, larger and more potent than before, forced Zaraki back, but he blocked it with a smile and a booming laugh.
"Haha! Fine, let's fight Ryou!" he shouted, charging at me as we clashed.
Our blades met, broken sword against sword, as we collided again and again. I was quicker, my reflexes slightly sharper, letting me evade his deadly strikes and counter. After dodging an overhead strike that would've cleaved me in two, I seized the moment. "Cursed Slash!"
The blow barely made him flinch, pushing him back only slightly, but his grin widened with each strike. I dodged one of his sword arcs, as massive as my Nemesis Cursed Slash, with Shundō.
Time seemed to still in Muken. Or at least, it felt that way—no indication of how long Zaraki and I had been locked in combat. 'Not that there's a chance to check anyway.' Neither of us had a moment to breathe, he'd managed to land two hits, one nearly cutting me in half, the other almost severing my left arm off. Each time, I had to run Muramasa along the wounds to cauterize them, a temporary fix, but it would have to do. I tilted my head as Zaraki's blade missed my cheek by inches, retaliating with a counter.
"Nemesis Cursed Slash!" My attack landed across his chest, pushing him back slightly. 'Fucking monstrous durability.' With an enhanced Shundō, I dodged as he countered with his own massive sword slash.
The battle went on and on. If I had to guess, we'd been at it for six hours. In that time, I'd learned more about cursed magic than I ever expected. Cursed magic worked almost like a battery, it could hold a certain amount of power without draining over time, provided it was internally focused. Splitting the energy half into Muramasa and half into enhancing my body lessened its effectiveness, but directing the entire output to one or the other boosted its potency. Only when channeled externally, like into Muramasa or offensive techniques, did the reserves actually deplete.
But the real challenge? Reiatsu. Cursed magic and Reiatsu were preventing each other from being used properly. Sure, I've used both at the same time, but the attack wasn't as powerful as it should've been. 'Wonder why I haven't done this in the first place.'
I leapt away from Zaraki, blocking his pursuit with a sword slash, and took a quick, much-needed breath as he shrugged off the blow. 'Half my cursed magic left. Hopefully, it's enough.' I stopped channeling cursed magic into Muramasa, redirecting it all into my body to push my physical limits even further. 'One thing it doesn't do is boost my stamina.'
Smiling at Zaraki, I watched his grin widen, his laughter echoing through Muken. "Ryou, I haven't had this much fun in decades!"
I let out a snort, letting my Reiatsu flood into Muramasa. Black, red, and purple aura erupted around me in a chaotic blaze. "This is only getting started, Zaraki!"
{Author's update regarding DxD}