Author's Note:

Hello everyone, this is my first fan fiction ever, I hope you like it. If you do or if you don't, please consider leaving me feedback so I can improve. A couple notes:

I use a few Japanese phrases such as '–chan' and Mokuba sometimes refer to Seto as 'Nii-sama' which means big brother because he says that so often in the Japanese episodes

I'm afraid I couldn't find a spelling for Seto's adoptive father, the subtitles had it all wrong, and so I spelled 'Gosabouro' phonetically.

Mokuba groaned and sat up, instantly regretting it. Holding a hand to his temple to dull the dizzying pain, he opened his eyes. "Where...am I?"

"Why, you're here of course. Don't you remember?"

Mokuba sat bolt upright and snapped his head around to find the source of the voice. "Who are you? Show yourself!"

"I'm right here silly boy. But you don't know where 'here' is, do you?" the womanly voice said again.

Scanning the room and finding nothing, he looked forward again and nearly fell over. Crystal blues eyes stared at him intently. "Wah! Wh-who are you?"

The girl stood up to her full height and stared down at him for what seemed like forever. By her height, Mokuba would've guessed she was in her late teens. Finally she smiled and in one smooth gesture brushed her hair back, tucking the eye-length blond strands behind her ear. "You can call me Lillith. But I'm not the one you should be concerned about, what about yourself?"

"Me?" It was then that Mokuba took note of his surroundings. He was in some sort of foyer, where white and scarcity seemed to be the theme. Simple patterns of light blue and white spread out on the floor, with two pillars next to either wall. Behind him loomed a red door within a giant frame at least ten feet tall, decorated with golden insignias. Ahead was a small red-carpeted staircase, with a golden, double-door crown. "Where...where is this?"

"Hmmmm. This place is called Castle Oblivion, Mokuba. And since you agreed to come here, I'm afraid you can't leave until you finish."

"Castle Oblivion? Wait, I never agreed to come here!"

Lillith grinned, "Yes you did. Maybe you know this place by another name, Memoria Catena Moenia."

Dark mist rose from her feet and enveloped her body. She was still grinning as she faded from view. "Wait! Don't leave me; I don't know what to do," Mokuba cried out.

The panicky boy sprinted towards the darkened space but the mists parted and disappeared before he even came within an arm's length. Carried on the same breeze that dispersed the mist came Lillith's taunting voice: "Then I suggest you find out for yourself Mokuba…and soon."

He ran right through where she had been but a moment ago. He couldn't believe it. His mind tried to grasp how she disappeared like that, but wasn't having much luck with logic. What just happened? Some kind of transporter…a worm hole? That would explain the darkness. Wait, that mist, I've seen it before. And that name "Memoria Catena Moenia". That name tugged vaguely at the back of his mind, but he couldn't quite place where he knew it from…

Nii-sama! Mokuba exclaimed excitedly. Seto would be looking for him, right? He looked around frantically and started calling for his brother "Nii-sama! Seto! Where are you big brother?"

Getting no answer, Mokuba leaned against a pillar in defeat, there was no one here…or at least no one that wanted to be known. Taking another look around, his eyes settled upon the red door atop the stairs, the only colored thing in the room. Walking up to it, he tried to make out the insignias surrounding the frame, but none held any meaning to him. He ran a hand across the door, finding it surprising chill. Feels like wood…no way I could break it down.

A glint caught his eye. To the right of the door was a golden plaque with an inscription.

If thy wish is to enter here,

reveal the memory most dear

Much can be learned, limitless thought

Exchanged for what you have been taught

Traveler beware

"That's more than a little ominous," he mused. Hoping for better luck, he crossed the room to the other door. This one wasn't adorned with anything but a large deadbolt. There was no sign of rust but no matter how much he pushed or pulled, the bar didn't move. "I guess I'm not supposed to go that way."

Returning to the exit atop the stairs, Mokuba tried everything he could to open it. Pushing didn't work, neither did kicking, even 'open sesame' failed. No matter what he did, the door would not budge. Frustrated to tears, Mokuba raised his fists high and brought them down hard against the door. "Why bang won't bang you bang OPEN?! BANG " he shouted without reservation.

Mokuba put everything he had into that last pounding. Now he felt cold and empty inside, and outside his arms and hands throbbed with pain. A single convulsion opened the flood gates, with one rattled breath. Before he knew what was happening, salty tears started to run down his face and mucus clogged his nose. The boy's body slid down to the floor when his legs buckled. The only sound in the room came from that ball of clothes, openly weeping.

A while later Mokuba felt better, crying it out really helped. I'm not a baby anymore, I can't just sit around crying, what would brother thing? Besides, he told himself, I'll never get out of here by staying here. His resolve formed, the younger Kaiba wiped his eyes clean and reached into his collar. What he pulled out appeared to be a framed Duel Monster card on a cord. Nobody ever took notice of it, even though it was always on his person. Just as well, for the card was really part of the key to the Kaiba Corporation. Even Pegasus, who once had Mokuba within his grasp never suspected. Of course no one knew about its more benign function either: as a locket. With a flick of his thumb over a hidden latch the locket opened, revealing a photo. Mokuba smiled weakly as he gazed upon the familiar picture. In it an adolescent Seto was smiling, holding a chess piece. Mokuba remembered that moment all too well. It was the last time his brother's smile had been filled with genuine warmth and happiness. "Brother…"

Mokuba was overcome by nostalgia. The chess piece Seto was holding was about to take his younger brother's pawn. They were in an orphanage after their parent had died, before Mokuba had even heard of Gosabouro's name. His brother wore those clothes because they had nothing left to wear and he's glowing because—wait, glowing? Indeed, the entire picture was giving out a soft light. The more he focused upon it the stronger it grew. Until what began as a dim glimmer became as bright as a flashlight in darkness. "This is…"

Whatever thought he was voicing was interrupted by a loud creaking behind him. Looking up in surprise, his eyes widened at the pitch-black rectangle he saw in back of him. Reflexively, Mokuba turned around and scooted back to the top of the stairs. The door had opened!

Regaining his wits, Mokuba examined the two door halves. They had opened outward and showed no signs of being forced…or any type of locking mechanism for that matter. It all seemed really occult and suspicious…but what choice did he have but to go onwards? It wasn't like this was the first weird thing he's seen in this castle.

Tentatively Mokuba stretched out his hand and pushed a single finger past the threshold of the door frame. The darkness covered the invading digit completely. Fearful, he drew it back. Rotating his hand in front of his face, he could find nothing abnormal. With one last scan of the room, Mokuba drew himself up and gathered his courage. Looking forward Mokuba stepped through the door, into the unknown.