I tend to feel Sonic stories ought to have a 'version of reality' explanation attached to them, there's no many variations of canon. So for the record, this is set in the Fleetway comic universe, shortly after issue 178 "Splashdown".
For those unfamiliar with the series, a very brief summary of the background to the story:
A creature called Chaos was attempting to absorb the Chaos Emeralds. Sonic and friends fought him and one of them, Johnny Lightfoot was killed. Feeling guilty, Sonic left the others and went off on his own. Meanwhile the creature went to the Floating Island. Knuckles was unable to stop him from reaching the Emeralds and was forced to jettison them, causing the Island to crash into the sea. Knuckles, also in a fit of guilt, wanted to go down with it, but Amy Rose knocked him out and they left with Tails in his biplane. Shortly after they got back Sonic returned and they all resumed looking for the now scattered Emeralds.
"Hiraeth" is a Welsh word. It doesn't have an exact translation. It's sometimes translated as "homesickness" or "longing" or "nostalgia" but it means a bit of all three and none of them really capture the original sense of helpless miserable displacement or the intensity of the feeling adequately. One suffering the hiraeth grieves for a lost place and time as for a dear lost companion.
Knuckles stood on the clifftop, silhouetted against the silver of the lake beyond. He was so close to the edge that Amy's breath caught in her throat. She didn't dare call out for fear of startling him right off it and she was caught by the sudden, horrible realisation that that might be what he intended in any case.
She struggled with herself, wanting to both shout to him and to keep quiet. In the end she compromised and walked out silently towards him.
Well, almost silently. Knuckles' hearing was acute and he turned while she was still several yards away. He scowled, but Amy was relieved to see none of the desperate intensity in his eyes he'd had as he insisted furiously that they leave him on the rapidly collapsing island. Instead he looked tired. Far too tired for someone who had decided to go for a walk in the middle of the night.
He followed her gaze to the drop, and gave a sharp laugh.
"It's all right, Amy, you don't have to hit me over the head this time." He stared down. "I don't know if I could fall anyway. You can't kill yourself by holding your breath, after all. Your body won't let you. Would mine let me fall instead of glide? Could I choose not to, right up until the end?"
He spoke in a flat tone, as if the question were nothing more than idle curiosity, and Amy shivered in spite of the warm night.
"Knuckles, come back from the edge. Please." She moved a few steps closer. "You're making me nervous."
Instead of obeying, Knuckles sat down where he was, feet dangling over the cliff edge to swing loosely against the rock.
"Sometimes I'd go to the edge of the Island and just sit, looking over. Wonder how high we were, how long it would take me to glide to the surface, what was down there." He watched a stone, dislodged by his boot, skitter and bounce down out of sight. "There was always something holding me there though. The Emeralds. My duties. A purpose."
He raised his head from his contemplation of the moonlit view and looked directly at Amy.
"What's holding me here?"
Amy stepped forward and took his arm. "Knuckles, come on back. This isn't helping."
"I didn't ask for help!" Knuckles snatched his arm back and leapt to his feet.
I didn't ask to be followed! Leave me alone."
"No." Amy planted herself firmly in front of him. "You want to know why I followed you? Hmm? I'll tell you. I was scared to death you were going to do something do something stupid. That's why." She glared at him, though noting at the back of her mind that at least he was now away from the edge. "Since Johnny died and the Island crashed, we've nearly lost Sonic and you both, and we can't afford to lose either. Especially not because of your great big stupid egos, which won't let you deal with the fact that you've screwed up for once! Well, you know what? That happens to the rest of us all the time!"
She paused to draw a shaking breath and was surprised to find that Knuckles' voice also shook.
"You think that failing my trust as Guardian is nothing more to me than bruised pride?" There was an icy undercurrent in Knuckles' voice. "I had believed you thought better of me that that, Amy. I certainly expected that you thought better of Sonic. He lost a friend."
"So did I!" Amy shouted. "And I stayed! I carried on! I didn't wallow around in my own self pity letting everyone else worry about me!"
"Sonic did come back," Knuckles pointed out, subdued by this outburst, the anger in his voice ebbing away.
"Yes," Amy conceded with a tight smile. "And I didn't even have to hit him over the head. Mind you, I've felt like doing it a couple of times, since. But we all still need him. And you."
"You don't need me. You never did before. Any of you. You all fought and survived long before you knew I even existed." Knuckles shook his head slowly. "I'm worn out. I've got nothing left."
"You don't mean that." Amy shook her own head in denial. He couldn't mean that. Sure he'd lost it a bit on the Island, but he'd thanked her afterwards for not leaving him. He couldn't --she wouldn't let him-- slip back into that frightening suicidal despair.
"I didn't think it would be this hard." Knuckles paced back and forth, his mouth moving as though he was trying to work out the words. "Have you ever been lost, Amy?"
"What?" Amy was baffled by this sudden turn in the conversation.
"I mean really lost, on your own, not knowing where you were?"
Amy frowned, "Well, yes. Once or twice."
"Then you know that precise moment when you realise you're lost? The fear. Confusion. Trying not to panic because if you give in to the urge to run about looking for something you recognise, you'll only get more lost."
He was looking in Amy's direction but seemed to stare straight through her. She nodded anyway.
"It feels like that every day. Every hour. Ever since the Island sank I'm adrift. I'm lost. Every time someone talks to me I jump because I don't expect anyone to be there. Every time I go outside I'm confused because it's not the view I was expecting to see. I can't sleep. I wake up every two minutes thinking there's someone too close to the Emeralds because there's so many people nearby. Then I wake up further and realise they're gone, then wake up all the way and realise they may be gone forever."
His voice grew quieter.
"And I'm afraid. What if it isn't just guilt or--" he snorted, "--wounded ego. What if this is what happens to Guardians who fail in their task. When the bonds between Island and Emeralds and Guardian are broken. What if I never find them again? What if this feeling never goes away?"
As if too exhausted to say any more, Knuckles fell silent. Dismayed by the desolate picture he made, and unable to think of anything to say which would be remotely comforting, Amy fell back on pragmatism.
"Come on," she said briskly, taking his arm again. "There's no point thinking like that. We're going to find them." She pulled firmly, and started walking back down the slope. "Come on back, you can sleep at my place if the base is too noisy for you."
She was expecting more resistance, but Knuckles seemed too dispirited to bother, and let her lead him without comment. The moon had set by the time they arrived outside her small house and Amy fumbled the door open.
"You'll have to sleep on the sofa I'm afraid, I don't have a spare room." She was aware she was chattering rather inanely but Knuckles just followed where she pointed and sat down.
"Do you want something to drink, I usually heat up some milk before bed for myself."
Knuckles shrugged and Amy moved out into the kitchen and poured enough for two into the saucepan. Her hand hovered at the door to the medicine cupboard. She spent a fair amount of time being the make-do medic to the group and had an extensive stock. Knuckles would certainly refuse something to help him sleep, but just as certainly, he needed it.
Amy silenced her conscience, selected a small sachet of power and dumped it in a mug. What he didn't know wouldn't hurt him. She fetched a second mug for herself and poured the milk. She stirred a spoonful of honey into both and carried them through.
"Here," she handed Knuckles the dosed mug. "Best bedtime drink going."
He still hadn't said a word since they'd come down, but he did drink and finish the mug. Amy fetched a blanket and put it beside him.
"Will you be comfortable enough?"
No answer. Amy sighed and went out into the kitchen to wash up the mugs. By the time she came back in Knuckles was asleep, still sitting up, head lolling back.
"Great." Amy muttered. "You know the polite thing to do would have been to lay down first and save me some trouble."
She eased him over onto his side and tucked his feet up onto the sofa. She thought about taking his shoes off but it seemed too personal so she settled for draping the blanket over him and creeping up to her own bed.
Amy woke to sunlight streaming through the window and someone knocking hard on her door. She scurried out of bed and rushed down the stairs. Knuckles was still flat out on the sofa, either the dose was stronger than she'd thought or he'd been even more exhausted.
She flung open the door to see Sonic all but bouncing on the doorstep. She joined him outside and closed the door.
"Pipe down, will you? Knuckles is sleeping."
Sonic eyebrows nearly shot off his face. "Huh? Oh. Well. Um... Actually that answers why I came round. He wasn't at the base this morning. Porker was worried." Sonic composed himself and stared unabashed at Amy in outright curiosity, a smirk starting to spread across his face. "So Knuckles is asleep in--"
"On the sofa, Sonic!" Amy wasn't certain whether her annoyance quite kept the blush off her face.
"Uh huh." Sonic grinned. "And is he likely to be favouring us with his sunny disposition today?"
Relieved as she was to see Sonic more like his usual, teasing self, even with those oddball green eyes, Amy frowned a little at the question.
"I don't know. I --" She paused. 'Followed' was not the word she wanted to use. "--ran into him, last night. He hadn't been sleeping well, that's why he's here. The base was too noisy. " Any more than that felt like betraying confidences. She doubted Knuckles would have said as much, even just to her, if he hadn't been so exhausted. Emotions were so much harder to hide when you were tired.
Sonic clicked a radio, "Porker? Nah, it's all right, he's here." He smirked at Amy. "I'll leave him to catch up on his beauty sleep then shall?"
"You do that," Amy returned, but with not real heat in it. Sonic had teased her as long as she'd known him, and needled Knuckles ever since he met him. It was when that changed that she worried.
She went back indoors and started making a quiet breakfast in the kitchen. For once she had nothing much to do. Until they found either the Emeralds or some trace of Robotnik, there really was nothing to do. It should have been a pleasant change, but instead she found herself restless. She tried to settle to a book, tidied up a bit, wandered outside for a while, had a light lunch and made another attempt at her book.
It was some hours after noon before Knuckles stirred.
Amy put her book down and instead of going into the other room, got up and starting putting her breakfast dishes and drip-dried mugs from last night away. She knew Knuckles would be able to hear her, and it would give him the option to slip away quietly if he wanted to.
Instead he came quietly to the doorway.
"Good morning," Amy said, lightly.
Knuckles looked at the sun out of the window.
"Afternoon, I'd say."
Amy shrugged, "Well you looked like you needed to catch up on a few nights worth."
"Maybe." He looked dishevelled and, if anything, rather embarrassed, but at least the desperate, crushing weariness seemed to have lifted. He even smiled a little as he asked, "Are you sure you didn't use the crowbar again?"
Amy smiled back. "Do I need to?"
"No." He met her eyes. "I'm sorry. Thank you. Again."
Amy shrugged, wanting badly to change the subject.
"Sonic came by. Porker was worried when you weren't at the base this morning."
Knuckles face shadowed and Amy wished she hadn't brought that up. Porker had been another witness to what happened on the Island and, finding Knuckles gone, had probably feared the same as she had.
He shook his head. "It's all right, Amy. I'm not going to 'do something stupid' as you so descriptively put it. I should go and talk to Porker though."
"Hang on, I'll come with you. He's probably going to need some help convincing Sonic to get his eyes looked at anyway. He's been dodging him for days."
Knuckles' mouth quirked slightly. "Have you considered--"
"--A crowbar?" Amy grinned. "Now that you mention it..."