Sorry if this isn't too in character to both Omori and IWLH, I rushed to get this down before I lost interest and let this story idea rot with the rest.

Time Lost Apart

"I kind of missed this." The voice of Kel rang into Omori's imagination.
Blinking, Omori noticed he was sitting in Kel's room. Oh...he had been spacing out.
"You'd always get lost in your thoughts like that, especially after we said something that caught your attention." Kel wistfully thought back.
"Man, you know I'm not smart like some of our other friends. Sometimes I wish you'd just open up and tell me what you're thinking." Kel interrupted.
Omori tilted his head.
"Can't you just tell me, just this once?"
...Omori thought about it. Well, he couldn't tell him all of it. But his most immediete thought at the time was of Hero and Mari. He could say a little.
"...I was just...thinking about Hero and Mari. It's sad that things ended up like that. I was thinking if they could get back together."
Kel spirits visibly lowered after that, and he thought of an odd amount of time.
"Kel?" Omori wondered if he said something wrong. He did, didn't he? Omori knew Kel felt bad about his part in what happened, but it wasn't his fault.
"Hero seemed really broken up. I never tried to talk to him about it. And Mari...well, she doesn't like opening up."
Omori nodded. "They were perfect for each other. I'm sure they can get together again."
Kel gave a sad smile, and stared at his desk. A photo of him, Hero, and Sally painfully visible.
...
This was going nowhere, but he didn't want to push it.
"Sunny?" Kel's voice jolted him.
"Yeah?"
"What if...they never get back together?"
Omori blinked. What? Hero and Mari were a match made in heaven. They're meant to be. Sure things might be rough from whatever Mari said, but she still loves him from what he saw in Headspace. And Hero has to love Mari, even after 4 years he couldn't let go in his own world. It wouldn't be any different here. Things couldn't have changed that much.
"What do you mean?" Omori responded.
Kel's eyes were incredibly unlike him. "I mean, I want them to get back together as much as you do, but it's been 5 years since they split up. What if it's just been...too long?" Kel took a breath. "What if they've just changed too much?"
...Omori couldn't help but feel like he was really missing something. "Changed?" He asked.
"I-" Kel stumbled over his words. It felt like he was holding back something.
"Kel..." What could he say?
...
"It wasn't fair." Kel mumbled, before his voice picked up. "Sunny, you're 18 right now. What are you going to do?"
18? He already knew that, but-
"You lost 6 whole years. We were just kids. Just the past few days we had been eating dinner at my house, talking about the recital. A few weeks ago we were sneaking out to Hobbeez. There was so much we could have done, and then you tripped down the stairs and suddenly you're 18."
At least, that's how it seemed. He lived out 4 years locked in his home before making the mistake of inserting himself back into their lives before the inevitable. It wasn't that staggering of a leap, but...he still lost out on 2 years. Omori didn't say anything, so Kel continued.
"Sunny...why aren't you mad at us? At me?"
Why would he? "Why would I?"
Kel took a deep breath. "Didn't Mari tell you? We stopped visiting only a year in. Basil and Mari were the only ones who kept going. I stopped because...I just couldn't stand it. Seeing you asleep every single day, hearing you'd wake up between tomorrow or never, it sucked. Whenever I tried to talk to Mari, she'd always drag me over and I had to see you like that." Kel looked over at Sunny, something between pain and relief.
"I stopped going because I couldn't. I just...couldn't. You were 13 by then. A whole year we could have been hunting bugs, running through the streets, reading comics, going to school together, being friends, you lost al of it. And how much more would you lose? Sunny, it's been six years."
Six whole years he was in a coma. It was a lot of time. He didn't really give it much thought since he's focused on helping Mari, but...
"Sunny, part of me didn't want you to wake up."
Omori suddenly looked at Kel. What?
"We split apart. I barely see Aubrey and Basil these days, even Hero. I got new friends in basketball, and I see them almost every day. All that time I spent with them...I missed you guys." Kel's face...he had never seen him like this. Would his Kel look like this at his funeral? "And now you're awake, from 12 to 18. And you have so much to catch up on, we have so much to catch up on. The 6 years we spent without you. 6 years you didn't have. We were only 12. It wasn't fair. I didn't want you to wake up because you lost so much. Being with you again has been so fun, but it also reminds of what we don't have anymore. All of us. Sunny, what do you have? How can you seem so put together with all of this? It hurts to think that we just fell apart. I've...things are't going to go back. Even with you back. I don't think that-"
"Kel!" Omori suddenly shot in, not wanting this conversation to go on.
"Sunny." Kel looked right at him, on the verge of tears.
...
"I..." Omori couldn't answer. He...didn't want to. Six years...six whole years. He just...wanted to help Mari. She was still the same sister he remembered, if really hurt by what happened. He was certain she could go back to being friends with everyone, even in her dreams she wanted that.
Headspace...they were always friends there. Nothing changed, they were the same kids they always have. Omori never had to think about these things ever. But they had changed. Aubrey had become a delinquent carrying a nail bat where a plushie had been. Kel was more mature, but also had gotten new friends. Hero seemed put together but really, really missed Mari. And Basil was wracked by the guilt he left him with.
How did they change in this world? It was even an extra 2 years apart. What if things couldn't go back? What if he was in way over his head? What if things fell apart that much? What if they couldn't get back together, not even Hero or Mari who loved each so much? What if...Mari couldn't be...
Omori was beyond thankful for his usual poker face never betraying a hint of emotion even at the worst of times. He pulled himself together to say
"I never really thought about it...but it doesn't bother me. I'm just glad you're all okay."
Part of him thought that responding so calmly and nonchalant to everything Kel said would make him explode.
But it felt more like the air was let out of him. Kel almost visibly deflated. And after a moment of silence, began to laugh.
"Ha-HAHAHAHA! S-Sunny..." Kel started rubbing his eyes, even if there were no tears. "What's up with that?"
After a few more laughs, Kel elaborated. "It always felt like you had everything all put together. Maybe Aubrey was right about me making things so complicated." Kel stood up and reached his hand out which Omori grabbed. "How about we get some food and wind down?" Grinning all the while.
Omori felt so overwhelmed by the last couple of minutes that he could only take Kel's hand and stand up, following him downstairs.
Kel really flipped on a dime. If he didn't know him, Omori would have thought he was being disingenuous.
But he really is the Kel he knew, from both before and after.
...
18 years old...he really lost out on 6 whole years of his life. The rest of his childhood, he was an adult now. To tell the truth, it truly didn't bother Omori. He knew once things were fixed up and Mari was friends with everyone again, he could finally have the rest he sought after. He didn't have to worry about it. All he had to worry about was Mari. He should head home soon, she must really miss him after a long day.