Senkaimon

At the top of a large tower, was lime green unending courtyard that seemed to stretch almost boundlessly. At its edge was a red giant gate situated within a large tower at its peak. The place seemed to be near empty with it only being protected by very few Soul Reapers who wore long white face coverings.

"Is this really it? The top of this place is huge."

Kai's eyes opened with widened surprise. He looked back to see Yuki's reaction but she still remained nonchalant about the whole thing.

Eventually a Kido corps member approached the two, with a bird cage in hand. Inside it were two hell butterflies.

"You're going to need these." The corps member said, as they opened the bird cage.

One of the butterflies left its cage and immediately attached itself Yuki, but the other remained inside. The Kido corps member tried to get it out gently but it refused. 

"How strange?? Give me a second here."

They then ripped the cage in half with pure physical strength which scared Kai a little. He then quickly grabbed the butterfly and then stuffed it in the palm of Kai's hand.

In that moment he took notice of Kurenai, who was resting on Kai's shoulder as he always has been.

"Is that a hell butterfly on your shoulder?"

"No? Aren't they black? This one is red."

The Kido Corpse member zoomed in on Kurenai, investigating every part of it, without even touching it.

"I've been working with hell butterflies for years, so I know when I see one. They are all usually kept within Squad 4s barracks or the Kido floral room where they're bred. Maybe this is a new mutation or species?"

The Kido corps member took great interest in the butterfly, and tried to reach out to touch it. But then Kai quickly slapped his hand away.

"Kurenai has been with me ever since I got here. I would prefer if you didn't touch him."

He rubbed his hand, and apologised to Kai.

"This way please."

The Kido corps member, guided the two towards the Senkaimon gate all while still hiding their face behind that white veil. He signalled for the two other Kido corps members who stood next to it, and then they started to chant something. 

A couple seconds later, the gate began to open, and its contents were filled with a bright blue light. Tightening his breath Kai prepared to return to the world of the living.

He took one step inside the light and felt his whole entire body getting sucked in, and then within that same second, he felt his grip around the hell butterfly weaken as it then flew away.

The Kido Corps member quickly tried to pull Kai back out but it was too late for him, as the light swallowed Kai and Kurenai entirely. Yuki quickly followed the two, positive in knowing that she could save the them.

"Shit! uhh... What do we do now??"

He looked to the other two who opened the gate, but they shook their heads denying all responsibility. Then as if the grim reaper had come to punish him for this great mistake, a voice they recognised all to well , as it was the voice of Byakuya Kuchiki.

"GET AWAY FROM THERE!"

Then in an instant, the ground beneath them erupted and tore apart, as a mass of a black liquid like substance, quickly devoured them all while also destroying the Senkaimon gate. Multiple yellow eyes then spawned from it, and they all simultaneously locked on to Byakuya Kuchiki.

The Squad six captain quickly unsheathed his Zanpakutō.

"Scatter, Senbonzakura."

His blade flashed with a bright pink light, before disintegrating into hundreds of thousands of cherry blossom petal like blades leaving only his swords handle behind. The wave of black Reiatsu charged towards Byakuya as he quicky created a storm of petals that tore it to pieces. But this wouldn't be enough to sop it.

The wave of Reiatsu overcame his Senbonzakura, and so he used Flash step to quickly jump into the sky without getting hurt. If he touched the Reiatsu overflow for even a second, he was sure to die.

He pointed the hilt of his blade at the Reiatsu flood, which caused numerous amounts of Senbonzakura petals to gather into spear like shapes, and pierce the Reiatsu all over, pinning it in one spot.

"Tosatsu no yari"1

The Reiatsu suddenly exploded, instantly dispelling petals that pinned it down, and started to climb in the sky as it rapidly approached him.

Byakuya used Flash-step to quickly avoid its advances and returned back to the ground. He then held onto his Zanpakutō in a reverse grip fashion before quickly returning all the cherry blossom petal blades back to its hilt.

He dropped the blade into the ground, which made it sink into the floor while creating a ripple like effect.

"Bankai..."

The sky turned dark, as two rows of a thousand giant blades rose up from the ground.

"Senkei Senbonzakura Kageyoshi."

The giant blades then deconstructed from its top to the bottom, as they turned into thousands upon millions of even more cherry blossom petals. They then gathered above the river of black Reiatsu which quickly approached Byakuya while it hissed at him.

They then gathered and turned into smaller swords, resembling pink glowing Zanpakutō numbering in the thousands. They each pointed its blade at the black Reiatsu.

"Aki."

Every single one of those blades, then fell on top of the Reiatsu, piercing it from all sides, as well as pinning it to the ground.

Several new Kido Corps members that followed Byakuya, then gathered around the Reiatsu and pierced several iron rods into the floor around it. They then chanted something while a voice which sounded like screams emanated from the Reiatsu.

Once they finished, a blue light connected each rod together, creating a pentagram like structure which dissipated the Reiatsu permanently.

Breathing a small sigh of relief, Byakuya grouped up with the others.

"Byakuya Kuchiki. I do recall asking that you keep it down long enough for me to study it."

Mayuri Kurotsuchi who wore very bizarre clothing aside from his Captains Haori said, as he approached him.

"5 people died because I couldn't get here in time. I'm not going to stall destroying it just for one of your experiments."

"It really was unfortunate. My idiotic department predicted it spawning in the wrong place so I will punish them accordingly. However everything I do is for the sake of the Seireitei. Its not like they all died anyway, 2 of them managed to pass through the Senkaimon."

He breathed a short sigh of relief before slowly leaving.

"Where do you think you're going? You need to compensate me for this! Yhwachs Reiatsu is a rare specimen that appears only once every couple of months. There is no telling when and where it will appear next."

Byakuya ignored his cries and continued to walk off.

"Don't ignore me! Kuchiki!"