When Seto Kaiba found out that the other Yugi was gone, and cancelled all his meetings that day to pace his office in a quiet fury, Mokuba rearranged his calendar to attend in his stead, and took careful notes. It wasn't that weird. Sometimes Seto got bolts of obsessive inspiration and disappeared, shut everything out and stayed up until 3 am and came out a few weeks later with blueprints for something to change the world.

It was weird when Seto built the Yugi simulation, ordered the VR artists to redo the hair seven times until they got it right, and dueled it over and over again. It was weird when Mokuba noticed, one morning, him pour half a cup of coffee onto the floor while missing the cup by several inches and staring into space.

So Mokuba made sure the cleaning staff did an extra run through the lab to collect dishes, and Mokuba told the parks division to send the concept art for the new coaster to him instead, and Mokuba called human resources and said no, don't actually fire that poor guy in animation. And Mokuba texted his brother, caught him at his rare breaks, annoyed him with Do you want to play soccer? Do you want to play chess? Did you sleep? Do you want to talk? which went ignored, mostly, but the stilted replies he did get meant Seto was in some way still tied to earth.

This was Mokuba Kaiba's job: anything that made his brother's job easier. Hovering at the edge of the doorway, CC'd on the email, quietly listening in to the conference call. A cheerful sidekick, a loyal confidant, and a dutiful right-hand man.

So if his brother wanted an excavation in the Valley of Kings, then all Mokuba wanted was to make his brother proud. And when Seto announced plans for a space elevator, the construction of which would be expensive and complex, and which offered no obvious benefit to a gaming and entertainment company, it was Mokuba who told the stockholders to trust in his brother's vision. He'd never let them down before, had he? You had to let genius work. Seto knew what he was doing, he was sure, and Mokuba's wide-eyed faith and sweet smile were so difficult to say no to.

And if Seto Kaiba was still short-tempered, quiet, absent-minded, still dueling his imaginary friend, clearly he just needed more time. Mokuba could keep going to the meetings, handle legal, handle marketing, handle distribution. Anything for his big brother. Anything at all, no matter how big, no matter how hard, anything in the whole world.

It was the duel links incident when Mokuba admitted to himself he was worried. It all seemed so lovely at first, the whole idea of it, the way Seto talked about connection and transcending language and distance and bringing the whole world together. Then he'd almost died. Would have died. Would have been a goner, if Mokuba hadn't been there to slam the brakes. Yet Seto wasn't bothered at all. He came out laughing, grinning like a madman, rambling about netherworlds and higher consciousness and things Mokuba only half-understood, talked only about quantum physics and the pharaoh, but Mokuba swallowed his fears and tried to trust him.

A tournament on a week's notice. A weirdo with a magic cube. Yugi's insistence that what he sought was impossible. A monster trying to drag them all into another dimension. But Seto Kaiba didn't give up! No, he never gave up, never let go of anything, not ever, and usually this is what made him brilliant and brave and cool and stronger than everyone else but sometimes, sometimes—and this was a thought Mokuba felt guilty for having—sometimes it made him very stupid.

Six months. Six months of his brother being irritable, distant, distracted, erratic. And now this.

So when Seto Kaiba stepped out of the elevator, still strapped in to his dimension-system gear, to see Mokuba standing next to the emergency shutdown switch, Seto was annoyed but mostly just confused.

"Mokuba." He was trying to sound patient. He was always patient with his little brother, even when he was mad, even when he was tired, even when Mokuba didn't feel like he deserved it. "What are you doing?"

Mokuba, though, was not confused. He was six months of desperate, three years of worried, a whole life of unfettered loyalty, piled up on top of each other until something just burst.

"What am I doing?" Mokuba asked, incredulous, hands balling into fists. "What are you doing?! How could you not answer me? Not say you're gonna come back?" It came out louder than either of them expected, a ragged yell that easily filled the tiny white room. Seto took a step back reflexively, in surprise.

He lowered his voice. Tears stung the edges of his eyes, and he was trying very hard not to let them get any farther. He stared at his shoes. "I know you miss him," The 'him' did not need naming. "and I know this is really important to you, but you're not acting like yourself! And...and I'm not letting you do this if you're going to leave me behind!"

"Mokuba, you're being—" and he reached up, unconsciously, to touch where his locket usually hung against his heart, and seemed to notice for the first time in weeks that he wasn't wearing it. He stopped midsentence, seemed to realize something, and there were gears turning behind his eyes. He shook his head, annoyed. "We'll talk about this later." He turned and addressed the staff. "Prepare the prototype for another run. We try again as soon as possible."

"Of course, sir."

"Seto!" Mokuba objected.

"I said later." and he turned and walked out the door, and Mokuba was left behind.