All rights belong to Akira Toriyama, Toyotarou and Toei Animation
This is based on the manga cannon, so there may be some discrepancies with the anime.
As it turned out, the intelligent and insightful angel did not, in fact, know 'what to do'. Bereft of any ideas, he had simply suggested Vegeta be confined to a reinforced room in Beerus's castle.
Goku wasn't sure what to make of the Vegeta they now possessed. And possessed did seem an apt word, now that he thought about it. The saiyan had tried to throw himself at Whis and Beerus without a thought when they had arrived, only being stopped by the fast-acting Goku.
He couldn't believe it. Vegeta had always been so cautious around Whis and Beerus, so respectful, and all that had clearly gone out of the window.
Vegeta had been turned into an absolute psychopath. He had not stopped throwing himself at the walls and door of his prison since being locked in there hours previously. Goku was pretty sure he had heard the bed being upended and launched, but that had no success either in the captive's bid for freedom.
After waiting outside for fruitless hours, Goku had left in search of a meal for himself and his friend. Underneath a tower of dishes, he returned to his post, contemplating how best to approach the delivery.
"Vegeta?" he tried cautiously, "I brought you some food."
This did not calm the raging storm inside the chamber adjacent, in fact, it seemed to make the demented howling and scratching even worse.
Goku took a tentative step towards the door, correcting the swaying food as he approached.
"I'm going to come in now, okay?" he tried again, "So don't attack me, or I'll drop your food all over the floor, and I know you don't like that."
Vegeta did indeed not like the disrespect of food, such a vital piece of the saiyan lifestyle. Attacking someone carrying food, meant for him no less, would be completely out of character.
Just like everything else about Vegeta at present.
Reaching out with a shuddering hand, Goku gently twisted the knob,
And threw himself rapidly into the room, slamming the door shut behind him to prevent his prisoner escaping. He really didn't like the idea of Vegeta being locked up, didn't think it was best for his recovery (and he would recover, Goku was positive). They had no choice, however. Vegeta had absolutely no boundaries at the moment.
The reinforced stone walls were covered with deep cracks, chips of stone scattered like confetti about the tiled floor. Goku was able, with his speed, to quickly take in the state of the furniture. The bed had been terribly mistreated, strips of linen hanging limply off a vertical bed-frame. Chips of wood lay around the forlorn piece.
The bedside table would need to be mourned, because he was sure that was the former life of the chunks of timber littered around the chamber.
Gosh, it was like Vegeta had been turned into a wild animal. He just needed that lashing tail.
He didn't get the chance to observe the bathroom's condition before a blur charged at him.
"Hey!" Goku cried out, trying to fend Vegeta off with one arm while balancing the food on the other, "This is your dinner! Be careful!"
That was where the animal analogy fell short, however, because Vegeta seemed entirely unconcerned with the meal – his one goal in life was to remove Goku's face.
"I'm just going to put it down, here," Goku tried, still as if speaking to a spooked creature, wincing as sharp nails pierced his powerful arm, "And then I'm leaving, all right?"
Food deposited, Goku was out of that room in a flash, shutting the door behind him sharply and leaning heavily against it as he fiddled with the lock.
"Good grief," he whispered to himself, staggering to the opposite wall and sliding down it. If Vegeta was human, he would certainly be confined in a lunatic asylum.
"What are we going to do?"
It was clear that Vegeta needed help, but no one strong enough was qualified to provide it. And there was no telling if a human psychologist would be able to assist, given the alien nature of the ailment.
Goku had heard that time healed all wounds, and he dearly hoped the saying was right about this crisis.
In the meantime, though, Goku was going to have to work out how to tell the news to Vegeta's family.
It was not something he was looking forward to.
It was a few days after 18 had left in a hurry, shouting at him not to follow if he valued his life (and their relationship). Everything had settled down. The darkness, whatever it was, had disappeared only an hour after his conversation with Goku.
And it was that conversation which was troubling Krillen. It left a feeling of guilt gnawing at his gut. No matter the extenuating circumstances, he should not have been so harsh on his friend.
As soon as he felt Goku's energy back on Earth, he bid his family farewell and took to the skies in search of his long-time buddy, a not-very-well practiced apology on his lips.
What he found, upon dropping down beside Goku in Bulma's backyard, was not the saiyan he had expected.
It definitely looked like Goku, but it certainly did not act like Goku. The dictionary picture of glum, 'Goku' was staring sightlessly at the gravity room. He let out an explosive sigh, but still did not seem to have noticed Krillen's presence.
"Um…" Krillen broke in, causing the figure to jump, staring at him as though he were a ghost.
"Hey, are you okay?"
"Me? I'm fine." Goku answered, facing the gravity room again.
"You're clearly not. Listen, if this is about our…ah, talk—"
"It's not."
"But even so, I wanted to apologise."
"No need." Goku cut him off hastily, "Besides, you were right about a lot of things. I have been neglecting my friends."
"It's okay, Goku, really. Priorities change, friendships shift."
"Krillen," Goku began, licking his lips nervously, "Are you still friends with Bulma?"
"Yes, of course!" Krillen wondered at the sudden shift.
"Oh good, because I think she's going to need some help right now."
Krillen didn't often visit Bulma, being busy with his own family, but he never failed to attend one of her numerous parties and appreciated the chance to catch up. If she needed him, he would be there, and he said as much to Goku.
"But why? What's happened?"
"Vegeta…" Goku began again, trailing off and shaking his head.
"Good grief, what's he done now?" Krillen asked in a long-suffering voice.
"I don't want you blaming him for this!" Goku replied with a fierceness with took Krillen aback, "It's thanks to him that we, and the Earth, are fine right now. But it came at a cost."
"He sacrificed himself?" This was not exactly a new strategy for Vegeta.
"Yes. But…not in the way you're thinking. You know that dark haze, the stuff which made 18 leave you?"
Krillen nodded, not seeing where the conversation was heading but feeling a sense of foreboding all the same.
"We…basically imprisoned it inside him. And it's sent him mad."
"Mad?"
"Yep, completely crazy. Psycho." Goku rolled his finger around his ear in a juvenile fashion.
Krillen reached up and patted his friend on the arm, "Geez, Goku, I'm sorry. I know you two were close."
Goku shrugged him off, rubbing his eyes tiredly. "He'll get better," he said, as though trying to convince himself.
Krillen did not say anything to dissuade his friend, but he was not so optimistic. This was not an injury they were dealing with, it was not something that could be fixed with the Dragon Balls, he thought, or the sensu beans. This was an entirely new challenge. And Vegeta might need care for the rest of his life.
What a terrible solution!
"Krillen, did I do the right thing?"
"Huh?"
"I…used the mafuba technique on him, to seal away the Darkness. He was so insistent, you know. But should I have refused?" Goku's eyes were desperate, seeking reassurance that Krillen couldn't give.
"I…can't answer that Goku."
"Bulma blames me."
"Should I talk to her?" Krillen asked, gesturing to the dining room, where he could sense Bulma's presence.
"You can try." Was Goku's pessimistic reply.
This whole situation was not what Krillen had expected from his day, and the sight before him even less so. Bulma was seated at the dining table, in a rumpled blouse, with fingers clawing through her dishevelled hair. Krillen had never thought he would see the self-proclaimed beauty in such a state. Her make-up was smudged about her face, giving it a bruised look.
She didn't acknowledge him as he entered.
"Hey, Bulma," he greeted with false merriment.
"Shut up and go away." Bulma ordered in a low voice, an instruction completely ignored by the short man.
"Nope," he said cheerily, pulling out another chair and seating himself in it.
"Leave me alone." She tried again, with just as much success.
"I heard about Vegeta," Krillen attempted to keep his tone light, and thought he might have even succeeded.
Bulma merely rubbed her eyes, refusing to reply or look at him. Finally, after a few moments of silence where Krillen wondered how to continue, Bulma filled the void.
"This is different from when he goes away. I know he'll come back, then. This time…he's not going to come back."
"Where is he?" Krillen wondered, realising that he could not sense Vegeta.
"He's at Whis and Beerus' place. Goku point blank refuses to bring him here. But here, his home, is exactly where he should be!" she slammed a hand on the table to emphasise her point.
"Why isn't he here?"
"Too dangerous, apparently. He just…attacks everything."
"Maybe it's a good thing he's not here, then, I mean—"
"In sickness and in health, Krillen!" his companion spat, "It's my nuptial duty to care for him, no matter what!"
"But Bulma," he reasoned, "He could hurt you, or Trunks."
"I don't care!"
"Really? I think you do. But even so, think about what it would do to him, if he ever regained his right mind."
Bulma sighed, dropping her unkempt head onto the table and conceding his point. Then, seeming to pull some hostess training from the depths of her troubled mind, she rose to make them both a much needed mug of coffee. As machine prepared, she stared off out the always-clean window at her husband's favourite haunt, which stood silent on the grass.
Unbidden, Krillen wondered if it would ever be used by him again. He hastily dismissed the thought, clinging to Goku's optimism, in spite of his own misgivings.
"It's my fault," Bulma whispered, pressing a button, making hot, fresh coffee pour into the mug Vegeta had given her years ago, before the calamity with Buu, before the subsequent years of comparatively domestic bliss. It had a pink crown on it, with the word 'QUEEN' printed in bold letters, reminding Krillen of what exactly Vegeta had been born to be. King, that is. How differently his life had turned out, settling down on a faraway planet and raising a family with an inventor, of all things, not a powerful warrior at all.
"How so?" Krillen asked, returning to the conversation Bulma was both trying and trying not to have, "I thought you were blaming Goku."
"I am! I'm blaming Goku, I'm blaming my idiot, but really, this is my fault. I…" she trailed off, splashing some milk into both their mugs as she considered what to say next. It wasn't until they were both seated back at the table that she found the strength and words to continue.
"I tried to kill Vegeta, Krillen."
"I'm sorry?"
"You heard me! I tried to kill him! He was cooling off in the gravity room after a big fight, trying to stay away from me I guess. I hacked into the system to turn on the communication software and…gosh, the things I said, Krillen. You should have seen his face! I destroyed him!"
This didn't sound very much like actually attempting murder to him, and he said as much to Bulma, only for her to scream back
"I locked the door and turned the gravity level up to 1000Gs!"
"Oh." That did sound much more like trying to kill someone.
"Was he hurt?"
"I don't think so." Bulma mumbled, "but when I realised my plan didn't work, I started to concoct a poison to finish the job. I was part of the way done when suddenly I came to my senses."
She drew a few hasty mouthfuls of hot coffee, wincing as she did so.
"I threw up in the bin," she confessed.
Krillen, however, was comparing this scenario with his own wife's reaction to the dark haze which had impacted them so much a few days previously.
"It was the darkness, right? That made you do it, I mean."
"Yes, but…I shouldn't have been so affected by it. I mean, he was really calm! Infuriatingly so, at times."
"People are different, Bulma," Krillen contributed, sipping at his own beverage with more decorum. Then a thought occurred to him, "Does Trunks know?" he could sense the boy along with Goten far from the compound, probably on one of their adventures.
Bulma shook her head, "I don't know how to tell him. I mean, how do you tell a boy his own father, who he admires like nothing else, has lost his mind? That if his father saw him, he would attack him on sight? Vegeta never really hit Trunks, even when they were training together. He may have been distant, but he was never violent, unless you count being violently angry. But even then, he just yelled. Trunks wouldn't understand this."
"Do you want me to be there?" Krillen really hoped the answer would be 'no', because that was an overly emotional conversation he wanted no part of, but he had to ask. Bulma was his friend, after all.
"No, but thank you for the offer. I can handle it."
"If you're sure. But I'll be around to check on you often, if that's alright with you? You really shouldn't be alone right now."
Bulma gave him a small smile, and he could tell just how much this whole situation had rocked her when she didn't protest that she would be fine, instead telling him she would appreciate the company.