Oneshot, lines indicate change in pint of view.

Ukitake tried not to cough when he was thrown back against the tree, the binding energy ropes tightening around his body. Having a coughing fit now would not end well. He managed to pull his arms up, so his hands were free, but the rest of his body was immobilized.

He glanced up at Kyouraku, who didn't seem to be in any immediate danger, then spoke a few kido spells to break the ropes. Which didn't work.
His Zanpakuto was still in his hand, but hacking at the ropes, careful so as not to cut himself, didn't do any good either.'
Ukitake suppressed the rare urge to curse.

They had been send out to deal with a small group of hollows, only the group was not small. Which should have been impossible, it were hollows after all, but there was one who was different, stronger, and seemed to be acting strategically rather than instinctively. And so, after fighting for a while, they had found themselves in this position.
Ukitake had been hit by the kido-like attack, and his Zanpakuto was useless now, unless he wanted to throw it at the hollows. At least he could still perform Kido, and so he spoke incantation after incantation, firing rapidly to keep Kyouraku's back clear. The Hollows were focusing on Kyouraku, as the currently most dangerous target. Kyouraku, who was fighting with only kido himself, after two of the hollows attacking in synchrony had disarmed him. Now his two Zanpakuto were lying too far away, useless as well.

They were managing so far, barely, but after destroying a few of the hollows now several with horn shields were advancing, and those were barely distracted by their kido.

Ukitake swallowed another curse in favor of thinking. And it wasn't all that hard to come up with a solution then, it seemed obvious. Also, completely forbidden, but what did it matter when Kyouraku was about to get hurt?

Sogyo no Kotowari, please make this work he thought, then he shouted 'Kyouraku, catch!', saw him turn, and tossed his Zanpakuto over, hilt first.

Never touch another persons Zanpakuto without their permission. Fighting with any Zanpakuto but your own is forbidden. These Katana have souls, do not play around with them.
Even if you just wanted to try it.
There have been Shinigami who got burned badly from stranger's Zanpakuto, Shinigami who could never talk to their Zanpakuto spirit again after another student used it.
A Zanpakuto has a soul, it is sacred. Do not disrespect it.

Kyouraku caught the Zanpakuto easily, even while his mind started to register what was happening. And while he did want to think, talk, or maybe just freak out right now, there wasn't any time, as he was still surrounded by hollows.
But he did have a Zanpakuto now, didn't have to fight with inefficient kido any more, and while he blocked the claw that sliced at him from the right, he felt himself smile.
The blade was slightly heavier than he was used to, but it still felt right in his hands, and his movements were fluid and fast. He didn't feel any pain from it, and Ukitake was still watching his back with kido, which meant he was fine as well.
He didn't know what Ukitake had thought, making that decision, but he felt a deep gratitude to him.

It worked. Somehow it worked, Kyouraku was fighting with his Zanpakuto as naturally as with his own, and Ukitake could still feel Sogyo no Kotowari's presence in his mind, calming, supporting.

They destroyed the hollows, one after another, with Ukitake's kido and Kyouraku's cuts.

Until the clever one was the only one left.

It was small for a hollow, and it's mask was unusual. Arrancar said the back of his mind, he had read something about those… but it didn't matter now.
Because the hollow wasn't bothered one bit by being the last one, and it didn't have to be. It was fast enough to dodge most of the spells and cuts, strong enough to block the rest, and it relentlessly fired cero at them. While Ukitake could raise kido barriers in front of himself in time, the blasts impaired his vision, and he rarely managed to shield Kyouraku.
Ukitake saw that his clothes were half burned, that he was already bleeding.

Sogyo no Kotowari. He addressed them, asking. He didn't have to elaborate, they could follow his thoughts.
Yes. We will protect him.

'Kyouraku, call Sogyo no Kotowari.' he shouted.

He was crazy. Yes, fighting with another's Zanpakuto was forbidden, and there were many scary stories, but he knew that some Shinigami had done it anyways, often without consequence. Using another's shikai… putting aside that it was so obviously forbidden no one even cared to say not to do it, it also was impossible.
'Impossible.' Kyouraku heard himself shout back.
'Trust me.' Ukitake said behind him. And he did. He would always trust Ukitake.

So when he heard Ukitake begin the shikai command he fell in without hesitation, speaking the familiar words he knew as well as his own. 'Waves, Become my Shield, Lightning, Become my Blade. Sogyo no Kotowari.' His voice mixing with Ukitake's.

Ukitake watched the blades separate, Kyouraku grasping the two hilts like he had always done it. Ukitake found himself surprised that it had worked, despite the fact that Sogyo no Kotowari had agreed. But it had felt like a good idea, and Kyouraku was hurting, so Ukitake had pushed them into Shikai as much as he could, and it had worked.

Kyouraku was used to fighting with two blades, though of different size and weight, and he seemed to adjust perfectly, and the hollow was finally looking worried.

And then it fired another row of ceros, and Kyouraku couldn't react fast enough to get out of the way, but he raised the left sword on instinct or maybe because he remembered, and Sogyo no Kotowari absorbed the energy.
Ukitake could feel it, though less extreme than when he held the blades himself, and he tried his best to control the flow through the red rope.
It had taken him long to learn how to modulate the energy, to control speed and strength of it, and now he just tried to keep it under control. He knew how much one could feel the backlash when holding the weapon. He didn't have time to shout instructions to Kyouraku, but Kyouraku was already pointing the right blade straight at the hollow, showing that he knew his swords ability well.

The cero shot from the Zanpakuto, straight at the shocked hollow, cracking his mask, and then he was disappearing as his his soul was released.

He released the shikai, checked that there really were no more hollows, and turned to Ukitake, who was leaning against the tree now that the energy ropes had disappeared. He looked very tired, probably having nearly exhausted his energy from all those kido spells, but he was smiling widely at Kyouraku.
Kyouraku carefully walked towards him and presented the Zanpakuto, arms outstretched, bowing as low as he could manage with his injuries.
He didn't know what to say, so he stayed in the bow even after Ukitake had lifted the Zanpakuto from his hands, even after he heard the sound of a Katana returning to it's scabbard. He just moved his hands into a traditional salute, and stayed.

There was a short pause, then Ukitake dropped into seiza in front of him, and looked up into his face.
'I'm glad it worked. Now stop being silly and sit down so I can start healing your wounds until the others arrive.' Kyouraku let himself be tugged down, while he scrutinized Ukitake.
'You, heal me? You are about two shakkaho away from losing consciousness from energy depletion. I can wait for the healers.'
And with that they were on familiar ground again, and Kyouraku went to pick up his own Zanpakuto.

They had send the healer that had accompanied them back to get help as soon as they had realized how many hollows there were. It was less that they had expected anyone to arrive in time, and more that the unseated young healer had stood no change against the horde and it had been the fastest way to get him to safety.
Still, Ukitake was glad when it didn't take long for a group of strong Shinigami that included two healers to arrive, and someone could start treating Kyouraku. While he did understand why he shouldn't heal him at the moment, Ukitake wasn't happy with it. Those wounds looked like they hurt.

They traveled back in a cart, and they both fell asleep quickly after it started moving.

The next day in the afternoon, two hellbutterflies landed on their hands, and they were asked to report to the head captain. Kyouraku made a show of moving slowly, carefully with his wounds while he got up, proving that he was well enough to play around, which reassured Ukitake.
They left the fourth division and flash stepped to head captain Yamamoto's office.

'Lieutenants Ukitake and Kyouraku. We read your reports of yesterday's mission.' they were greeted by Sasakibe upon entering.
'First of all: Lieutenant Kyouraku. Writing `There were lots of hollows, and we defeated them in the end. I'm sure Ukitake's report will be way more detailed than mine anyways, so I won't bother trying.´ is definitely not an appropriate way of reporting.'
Ukitake fought hard to keep from laughing, since it would be inappropriate in the situation, and besides he really shouldn't encourage Kyouraku any more.

Kyouraku heard Ukitake's breathing change, and he didn't even have to look to know he was trying not to laugh. He kept his face straight. 'My apologies, I thought it made sense. Are there any details you need?'
'Yes. Please confirm: you fought with lieutenant Ukitake's Zanpakuto, and activated shikai?'
Kyouraku shrugged. 'Well, I'm don't think I activated it on my own, Ukitake spoke the command together with me. And I did fight with the blades, but again Ukitake helped with the absorbing and releasing of the hollows cero. I felt him control the energy.' He didn't have to go into details, since Ukitake's reports were always quite detailed, they would understand.

'Impossible.' Sasakibe said, like he was stating a fact.

Yamamoto spoke up then. 'Obviously not. But certainly quite unusual. Did you know it would work?'
They both shook their heads.
'I never even fought with another Zanpakuto before.' Kyouraku added.

'But you wrote Sogyo no Kotowari agreed to it.' Yamamoto continued. Ukitake nodded. 'Yes. I asked them a few hours ago about that. They did not know it would work, just agreed to try.'

Yamamoto seemed thoughtful. 'Do you think it would work again?'
Ukitake shrugged. 'Probably.'
Yamamoto focused his eyes on him. 'Then please hand your Zanpakuto to Sasakibe. We will try this.'
'No.'

The answer came immediately, before Kyouraku had even finished processing the order. It surprised him slightly, coming from Ukitake. He didn't often refuse requests, and this had been more of an order really.
'Do you believe it won't work?' Yamamoto asked, still focusing on Ukitake.

'I do not know. I will not try it.' Ukitake said, voice firm.
Kyouraku carefully extended his reiatsu to surround Ukitake, to show his support in anything that might happen. Ukitake had his reiatsu low, very controlled, but he briefly extended it to Kyouraku in return, like a flash of a smile.

'Then why do you refuse?' Yamamoto asked, sounding strict.
Ukitake seemed to take a second to collect his words, then he looked straight back at the head captain and answered, voice certain.

'You yourself taught me that my Zanpakuto is a part of my soul, a part of me. I have since come to understand that for myself. How can you ask me to give that part to a nearly stranger? How can I even attempt to give it to anyone I do not trust to the fullest? To whom would you give a part of your soul?'

It was Yamamoto who lowered his gaze first. 'Thank you for making that clear. Very well.'

There was silence for some time then. Kyouraku was watching, unmoving, but his mind was shaking. He had understood that before, had known who incredible it was for Ukitake to have done that, and still, hearing that…was impressive.

'Then, will you demonstrate with Kyouraku?' Yamamoto asked Ukitake after a pause. It was a question, Ukitake knew 'no' would be accepted. And he hadn't meant to draw Kyouraku into this with his words.
He looked down. But Kyouraku's reiatsu was still surrounding him, supporting, unwavering. Ukitake looked at Kyouraku when he answered 'Only if he agrees.'

And this just made it even more amazing, Ukitake being willing to share his Zanpakuto again, even without a life threatening situation. Kyouraku smiled at him, trying to convey his gratitude, while he considered.
He questioned Katen Kyokotsu, and she send him silent agreement. Despite all the warnings and rules, it didn't feel wrong to use Ukitake's Zanpakuto, it didn't feel disrespectful.

Kyouraku turned to Yamamoto. 'I agree.'

Ukitake stood opposite Kyouraku, in the middle of a large training hall. Yamamoto and his lieutenant were watching from the side, but they were far enough away to give them some privacy.
Ukitake grasped Kyouraku's hand, letting his tight grip convey his seriousness. 'Are you sure?' he asked. Kyouraku held his gaze. 'I am sure. Are you?'
Ukitake felt his smile widen. Of course he was. He nodded, and released Kyouraku, stepping back and unsheathing his Zanpakuto. Then he smiled at Kyouraku again before presenting the blade to him on his outstretched hands, bowing low.
To show his respect for Kyouraku, and for both their Zanpakuto spirits. And his gratefulness to the other, both for agreeing to try it and for being someone he could trust this much.

He felt the weight of the Katana lift as Kyouraku took it, and straightened again, still smiling, returning Kyouraku's gaze that was intently focused on him.
Kyouraku bowed in return, Zanpakuto in hand, then he took the sword with both hands, moving into the position to call the shikai. Ukitake smiled, realizing how easily Kyouraku knew his Zanpakuto command. Not that Ukitake couldn't say Katen Kyokotsu's release command in his sleep.

'Waves, Become my Shield, Lightning, Become my Blade. Sogyo no Kotowari.' they said together, and then Kyouraku was drawing the blades apart.

They waited for Yamamoto and Sasakibe to walk to them, and waited more while the two older men walked around them a few times, staring.
'Do either of you feel any distress?' Sasakibe asked.
Ukitake shook his head. 'No.' 'We wouldn't be doing this if we did.' Kyouraku added, and Ukitake could see him rolling his eyes.

'What do your Zanpakuto spirits say?' Yamamoto asked.

Ukitake passed on the question, and answered first, since Sogyo no Kotowari was more present. 'They are comfortable.' he summarized, smiling.
They had said: 'We feel fine.' 'Since Kyouraku's nice.' 'but it's kind of boring' 'so can we play with Katen Kyokotsu?' 'Also, if we do this more often' 'we should start teaching Kyouraku how to use our abilities,' 'since last time the energy was really difficult to control.'

Kyouraku stood frozen for a second, after realizing he had actually heard Ukitake's Zanpakuto spirits talk. But he should not be this surprised, since he was holding their shikai form in his hands. So he noted the experience for later consideration and acted like nothing happened, asking Katen Kyokotsu the question.
'We agree with Sogyo no Kotowari. This is boring. We should either play or train. But we also don't mind you two sharing Zanpakutos, we are comfortable with their souls.'

'They also are comfortable.' Kyouraku said for the other observers.
Excluding Ukitake, whose eyes had widened while Katen Kyokotsu spoke, indicating that he could hear her as well. Kyouraku caught his gaze, and gave a small nod. They could talk about that later.
Though his mind was already reforming his theory. He could not just hear Sogyo no Kotowari because he held them, but because their souls were somehow in contact through them?
Still, it wasn't comfortable being examined, the way they were currently being examined by the leaders of the first division, so Kyouraku kept the thoughts to himself.

After some more time of walking around them and staring, Yamamoto nodded to Sasakibe, who told them to release the shikai. Kyouraku was surprised that they hadn't been asked to absorb energy of some kind, but he got the feeling that Yamamoto was quite surprised and Sasakibe was a little spooked by their ability.
They probably didn't want to push it. So they released the shikai.

Kyouraku directed a silent 'Thank you' at the Zanpakuto spirits, before again bowing to Ukitake, who took back his Zanpakuto and sheathed it. Then they bowed again to each other, both saluting respectfully.

Yamamoto ordered them not to tell anyone about this, which made a lot of sense considering that Shinigami often got hurt when using another's Zanpakuto. And with that they were dismissed.

They walked out in silence, and turned to a path that lead to the forest without having to discuss it.

'Well' Kyouraku said when they arrived at a clearing. 'As I see it, there are two things we have to do now.' Ukitake looked at him, relaxing when he heard the mirth in Kyouraku's familiar voice. 'Two? Go on?'

'One: I believe I heard a complain about me being bad at controlling the energy when Sogyo no Kotowari absorbs it. You should explain how it works.' Ukitake interrupted him, smiling. 'It's much easier to learn by doing, I will teach you.' Kyouraku grinned. 'Thank you, we will do that later. Before that, number two.' He loosened one of his Zanpakutos. 'It's your turn to try out mine, isn't it?' Ukitake stared at him for a moment, suddenly understanding exactly why Kyouraku had been overwhelmed when he had so easily given him Sogyo no Kotowari. That trust…

He saw Kyouraku's smile widen even more at his surprised expression, then Ukitake jumped forwards, laughing, and embraced Kyouraku, who laughed into his ear and held him close.

Before they exchanged their Zanpakutos again they stayed that way for a long time, content and at home.