A/N: Sorry this took so long. This fic is turning out to be more of a bear than I expected. Don't worry, I'm not abandoning it – my favorite part is yet to come!

Chapter 1: Monster Spirit Day

It had taken a year or so to figure out, but while it was disassembled, the doors and passageways of the Millennium Puzzle moved around in a pattern, a lot like the celestial bodies, only, more complicated. Knowing this made exploring a lot easier for Yugi, especially when he first went looking for one door in particular. It had taken another eight months to find it, but once he started making regular trips, the puzzle responded to his activities and adjusted to make the door more accessible.

Memories sprang up as the sandstone walls shifted to ghost-white on the way to said door. A few times, he almost turned to Atem to reminisce, only to remember he was alone. Yugi sighed as he grasped the door's handle. It was a good thing he'd tracked down this door. Otherwise he'd be going insane by now. And it had barely been three years!

The door creaked open into a black abyss. Not bothering to look twice, he jumped. There was a rush of darkness, then color, then it all cleared to reveal what resembled a fairytale kingdom. Green meadows and woodlands stretched out from a grand castle. In the distance, differing landscapes reared their heads or faded into the horizon. Cities, farmlands and villages dotted the entire scene. And Yugi was floating above it all (not far from a floating island) in a clear, blue sky. He smiled. The Monster Spirit Realm was a sight to behold. Much better than the Shadow Realm.

When he touched down on the meadow outside Spellcaster's Village, he realized how quiet everything was. Usually, when Yugi paid a visit, he would run into a few duel spirits right off. This time, everything was still.

"Anybody home?" he called after several minutes. Because, if he was being honest with himself, this felt like one of those times when he came home to discover Grandpa was out shopping –

Oh, boy.

Tears sprang up at the memory. It still hurt to remember him, especially since it usually lead to thoughts of the gang. Which in turn, could send him into a grief spiral. He shook away the memories in time, though.

He headed for the village square. "Dark Magician Girl? Anyone? Hello? Can anyone hear me?

The streets were deserted. He thought he heard an excited clamor off the main street, but when he arrived, there was nothing to see.

Yugi crossed his arms. "This is just weird."

"Yugi!"

He looked up at the source of the familiar voice. "Dark Magician Girl! Man, am I glad to see you."

She smiled down at him. "It's a good thing you called my name, or I never would have heard you."

"Heard me from where? And where is everybody?"

"Just hold on tight."

Hesitantly, he took the hand she reached down to him. "Why? What's going–"

They both vanished.

...

Mokuba smiled at the colorful costumes and bright faces all around him. He hadn't been sure what he was getting into when he accepted the invitation to "Duel Academy's first Duel Monster Spirit Day," but it had been worth the risk. So maybe it was one of Sheppard's weirder ideas. So maybe its real purpose was to keep a whole bunch of ancient magic in check. It sure beat sitting in the office. And he could tell the kids were enjoying it – if nothing else, this whole thing gave them a chance to be kids. Seto would have loved that. Whether or not he would have admitted it was another story.

An upperclassman dressed as Celtic Guardian pushed past him. "One side, pal!"

"Hey!" Mokuba scowled. As he stepped back to regain his balance, he caught sight of something through the crowd on his left. He turned his body fully to get a better look, eyes narrowing.

It was a head of spiky, black, red-tipped hair with blonde bangs. That in itself wasn't unusual – plenty of kid here were dressed up like the King of Games. Only, this one... didn't look like a costume...

"Yugi?" Mokuba whispered. Then he shook his head. "It can't be. That's impossible," he muttered. Only to mentally facepalm on remembering his adventures to date. I have seriously got to edit that word out of my vocabulary.

Still. Maybe he had finally worked himself too hard in trying to track down Yugi and was hallucinating.

Yeah, when has that explanation ever been right?

Someone behind Yugi's look-alike lifted his hand. Mokuba's eyes shot open. He could see that right through the look-alike's chest! It was the hallmark trait of a spirit.

"It is him."

Another student knocked into Mokuba, this one having the grace to apologize. When Mokuba looked up again, Yugi was gone.

Mild panic set in. Mokuba dashed for the place he'd seen Yugi's spirit. Wildly, he swung his head around for any sign of the spiky, see-through head. No. This wasn't happening. Either he really was seeing things, or he had actually seen his oldest friend for the first time in years, only to miss him. He wasn't sure which was worse. That's when he spotted something – someone – on the balcony of the Ra Yellow Dorm. It was him. Yugi.

"How the heck did he get up there so fast?"

He charged for the dorm, not daring to take his eyes from the spirit. Once through the front doors, it took him five minutes and directions from an RA to find his way. He burst onto to the balcony, out of breath. He sighed in relief to see Yugi was still there. He had his back to Mokuba, forearms propped on the concrete wall as he looked out at the students below. As his breaths leveled out, Mokuba realized they were alone. Perfect. He straightened, took another breath, and strode up to his old friend.

...

"It figures Yugi Muto's ghost would be haunting the Duel Academy."

Yugi looked up to see who had spoken. A dark-haired young man was standing behind him, looking straight at him. Not through him; at him.

"This spot taken?"

Yugi looked around, but there was no one else for the question to be aimed at. "You- you can see me?"

"Yep. Guess it must be that whole "bonds of friendship" thing that you and the gang were always talking about."

"Wait..." Yugi's eyes narrowed, finally registering the shaggy black hair, the half-smirk, and the familiar Kaiba stance. "Mokuba? Is that you?"

"You bet your duel disc it is! Now hold still!" Mokuba swung a fist at Yugi's shoulder. It passed through, throwing the Kaiba off-balance and sending sprawling against the wall of the balcony.

"Mokuba!"

The scowling Kaiba pulled himself up.

"Are you okay?"

"Aw, c'mon! That's just not fair! You disappear on us for almost three years, and then when I actually find you, I'm not allowed to punch you for it?"

Yugi flinched. "I guess I deserved that."

"And a lot more! Ishizu told me everything, Yugi – except where the puzzle was hidden. If she had, I'd have gotten you out of it myself years ago! I still can't believe she even let you do this!"

"Mokuba-"

"And this plan of yours! You know it's a one-in-a-million shot, right?"

"Um... that... didn't occur to me?"

"-And even if it does work, no one will remember you! You'll have to start from scratch! And they probably won't even be the same people! Ever think of that?"

Yugi rubbed the back of his head. "Yeah, I guess I didn't think this through as well as I thought."

"Darn right you didn't! And what about the rest of us? Aren't we your friends too? Rebecca and Serenity were worried sick! And Mai- oh, man. When I told her, I had never been more glad to not to be in the same room as her!"

Mokuba let the sentence hang. Yugi's head drooped. "I'm sorry. I just... couldn't handle the grief. Losing just about everyone I was that close to in less than two years..."

"And how do you think I felt?"

Yugi looked at his friend.

"They were my friends too, Yugi. Besides you, Leon, Mai and Rebecca, they were my only friends. 'Were' being the operative word. I made new friends. Connected more with Leon and Becks. Didn't let the past bog me down. My brother may not have been right all the time, but he was right about needing to move forward from stuff like this – and I lost him too! I'd say what you did is just the opposite."

Yugi sighed. "You're right. This was selfish and reckless. It just... felt like my only option at the time. I'm sorry."

There was silence, for a time. Mokuba leaned on the wall next to him, scowling. "I guess there's no point asking if there's any way to reverse this."

Yugi shook his head. "There's no going back now. Even if there was, I wouldn't have a body. As you can see."

Mokuba scowled and clenched his fists. At length, he sighed. "So never mind that. Just tell me where Ishizu buried the Puzzle. I'll call everyone together to dig it up and put it together again. Then we'll at least have you back where you belong."

Yugi grimaced. "It's not that simple, Mokuba. For starters, I don't know where the Puzzle is."

"You're kidding. You're supposed to be inside it for crying out loud! how could you not know where it is?"

"It's not like I can see out of it, Mokuba. I can hear things okay if I'm in the right place, but not enough to know where the Puzzle is buried. Especially since there's not really anything to hear."

The young Kaiba scowled. "There's gotta be some way to track this thing down!"

Yugi's expression was melancholy. "Even if you could, it wouldn't do anyone any good."

"And why not? I don't see why I couldn't put the Puzzle back together. I don't care how long it takes! And it wouldn't be just me. I'd have Seto's equipment and KC's research teams and the friends you left behind to help me solve it!"

Yugi sighed. "If you or anyone else alive right now put the Puzzle back together, you'd be able to access its power... but you wouldn't be able to see or hear me."

"What?"

I could influence the way the Puzzle is used, but other than that, you wouldn't know I was there. The reason it was different for me and Atem is that we used to be the same person. Two halves of the same soul."

"So... so what are you saying? That... that only Atem can really get you out of the Puzzle?"

Yugi nodded. "Or his reincarnation."

Mokuba stared, his mind struggling to process. Then his fists clenched again. An angry growl erupted from his throat. He brought his fist down on the balcony wall with a yell. "Dang it, Yugi! Why'd you have to go and do this?! It wasn't enough we had to lose everyone else? You had to go and check yourself out?"

Yugi turned his face away. "At the time, I figured if I didn't do this, I'd start considering suicide."

Mokuba looked at him in shock. "Please tell me you're joking." All the anger was gone from his voice.

Yugi shook his head, eyes closed to hold back tears. When Mokuba started going on about how Yugi should have told them, should have gotten help from someone, anyone (who wasn't a psychopath)... all Yugi could hear was the pain in his friend's voice.

That pain is my fault, he thought. And the others who are still living are going through the same thing. Because of my choice. How did I ever think this was a good idea?

Yugi's reverie broke when he realized Mokuba had fallen silent. After a moment, his friend spoke in a softer voice. "I miss you, Yugi. We all do."

"... I miss you, too. I'm sorry, Mokuba."

They stood there in silence for several minutes. At length, Mokuba's brow furrowed. "Wait a sec. You're supposed to be stuck inside the Puzzle."

"Yeah..."

Mokuba stood up straight. "So how the heck are you here?"

"It's... a long story."

"I've got all night."

"Okay, um... remember that whole situation with Dartz? How all those Duel Monsters were running rampant all over the planet?"

"Kinda hard to forget."

"Well, all those monsters had to come from somewhere, right? And I'm not talking about the cards."

"Let me guess. The Shadow Realm?"

"Not quite. It's an entirely different world called the Monster Spirit Realm."

"Monster Spirit Realm." Mokuba deadpanned. He tossed his hands in the air. "Sure. Why not."

"Atem and I found a door to it inside the Puzzle. It's how we found out about the Great Leviathan and the Legendary Dragons. We even connected with Timaeus while we were there."

"That's cool and all, but where exactly is this going?"

"After about a year in the puzzle, I decided to try and find that door again, and I did."

"So, wait. Are you telling me you've been spending all this time hanging out with Duel Monsters?"

"Well, more like half the time, but basically. Yeah."

Mokuba grunted. "Well... at least you're not alone, then. I was honestly worried you'd go nuts in isolation, like Noah did."

"Yeah, that was another thing I didn't really think about beforehand. Anyway, today when I visited, there was no one around. Then Dark Magician Girl showed up, and the next thing I know, I'm here. She said that all the positive energy these kids are giving off has been energizing all the monster spirits, so they were all able to cross the dimensional barrier."

"Wait, you mean like the whole Dartz thing we were just talking about?"

"No. Not quite. That time, the monsters were physical because barrier between realms had been torn open. That was caused by a full-scale attack in the Spirit Realm. Most of those monsters on the news were either refugees or so full of negative energy, they had no control over themselves. The barrier is intact right now, so only the monsters' spirits can cross. No one can see them, but that's not a problem, since the positive energy these kids are giving off isn't just attracting the spirits, it's keeping them in a good mood. Right now, they're just here to party, relax, and have fun."

"Woah. That's a mouthful." Now I see why Sheppard set this up. "So how come I can't see 'em?"

"Well, like I said. They're spirits. Not everyone can see them."

"I can see you."

"True, but I'm not a Duel Spirit."

"Can you see them, then?"

"Uh-huh." Yugi craned his neck. "I think the Ojama Brothers are photobombing someone down there."

"Heh. I wonder if they'll show up on the film."

"It's a possibility, I guess. There's a whole lot of magic around here, so I've been told."

"You got that right. This whole 'Monster Spirit Day' thing was actually set up to keep that magic from running wild."

"You're serious?"

"Yep. I guess Seto knew what he was doing when he hired Sheppard as Chancellor." He paused. "so how long does this last?"

"Until sunrise, I think. This energy may be strong, but Dark Magician Girl says it's only temporary."

"And I guess there's no point asking if you can leave the island, huh?"

Yugi shook his head. "I doubt this kind of localized energy would extend much further than the edge of campus."

Mokuba scowled. "Guess I'll have to wait until next year, then."

"Next year?"

"To see you again. What, you didn't think I'd miss a chance to see you again after three years tracking you down, did you? I mean, have you met me?"

A slow smile spread across Yugi's face.

"Wait a second," Mokuba mused. "Maybe it doesn't have to be next year. If I pull a few strings with Sheppard, I'll bet the school would host this more often! Like, maybe twice a semester or something."

"Um... well, I don't see how it could hurt..."

"Great! So whaddaya say? Next Monster Spirit Day, same place, same time?"

Slowly, Yugi smiled. "Sure. You got it."

Mouba grinned. "Fair warning, though – I'll be bringing company, and that company will include Mai."

Yugi grimaced. "She's gonna chew me out, isn't she?"

"Oh, you don't know the half of it. Rebecca's gonna want to say her piece, too. I'll have to remember to bring a video camera."

"...Well, I guess I asked for it."

"And don't you forget that."

There was a short pause.

"So... what have I missed?" Yugi asked.

Mokuba smiled.