Kira knew that, although Yusei Fudo was the responsible protagonist from the start—definitely more reliable than Jaden in GX—his development throughout the show was neatly portrayed.
Z-ONE admitted Yusei wasn't a King yet, but was the closest anyone in this world had come.
Remembering this, Kira suddenly asked, "If Yusei is the only one close to being a King in this world, then what about you?"
Yes, Z-ONE was someone from this dimension too. Few Yu-Gi-Oh! 5D's fans would ever doubt Z-ONE's might; some even believed he held back during the final battle against Yusei, never truly showing his full power.
Whether that's true or not, it shows just how powerful Z-ONE must be—many believe he was on a higher level than even Yusei by the end of 5D's.
Kira figured Z-ONE must also have attained the Duel King realm.
"Me…" Z-ONE's metallic shell echoed with a heavy sigh.
"Duel King… I did everything I could to reach that realm. But in the end, I was still too late. So what if you become King? In the end, I couldn't save or change anything.
What does being a King matter anymore? My time is almost up, no matter what."
Kira realized: Z-ONE probably had truly attained the Duel King's level, but now his body clung to life with the help of survival machinery. Even with all that, his time was almost gone.
He'd run out of time, couldn't bear the weight of the world anymore, and so excluded himself when discussing the strongest duelists.
"Only a King can become a savior. In the original history, Yusei Fudo was called a savior, a shining star who united people and brought hope. But he wasn't a King yet—so he couldn't bear the world's fate.
Without a true King, no one can shoulder the weight of the world."
Z-ONE's voice was loud, yet filled with weakness and resignation.
He looked at Kira. "I'm telling you all this because you're also a King. Even if you're a King from another world, our interests should be aligned for now."
Kira said, "I just want to prevent the collision of two worlds."
But Z-ONE shook his head.
"No—not just two worlds."
As he spoke, projections appeared in this white space.
Sphere after sphere, countless balls packed densely, all floating in boundless void.
Kira stared. "Is this…?"
"Worlds," Z-ONE said serenely.
"Countless worlds, each supposed to run in parallel—their histories flowing like endless rivers, never stopping, never crossing."
But just then, Kira saw that two spheres were drawing closer together, seemingly about to collide.
"Is that our world?"
"Correct," said Z-ONE. "Originally, my only goal was to prevent my dimension's future destruction. But things have changed.
Before saving the future, it looks like we need to prevent this entire dimension—from start to finish—being reduced to dust in the multiverse."
Kira frowned, thinking. "Why? Is it because history was changed?"
He had his doubts. Before coming here, Kaiba Corporation's observations showed that when a dimension's history was tampered with, the timeline would deviate from its original path, causing it to collide with other dimensions.
But in 5D's, Z-ONE and his team were constantly rewriting history, yet it never resulted in a dimensional collision.
"No, normally changing history doesn't cause this," Z-ONE explained.
"I've rewritten history countless times, and this never happened. Usually, if we change the past, the future simply branches into a new path—the old history is overwritten, and the new path becomes the official history, without generating new branches or alternate timelines. The process always stays on track."
He paused, his voice turning grave.
"But now, some other force has invaded this dimension—a dark, powerful force, just like me, capable of time travel and rewriting history.
But its changes have different effects.
Every dimension it manipulates falls off course, risking collision with other worlds. These altered timelines spiral into darkness—they become dark timelines.
And from these dark timelines, it gathers power. Each time it sends a world into darkness, it grows stronger."
"Driving worlds into darkness?" Kira frowned.
He recalled the Three Wicked Gods he'd tamed, who'd also said the world was destined to fall into darkness—words apparently passed on by that same extra-dimensional being who'd broken their seals.
"Exactly," Z-ONE replied. "For example, in a recently observed timeline, the dark entity meddled in history.
Originally, Yusei Fudo was supposed to lead the Signers to defeat the Dark Signers and save the world. But with the dark entity's interference, the Signers lost and Yusei died. That world fell into hell, ruled by the Law of the Netherworld.
A dark timeline was created, and the entity consumed all the despair and darkness from that world, growing even more powerful."
Kira's eyes widened. "So, destroying history and feeding on fallen worlds—that's the root of the dimensional collision?"
Suddenly, it made sense.
When he first arrived here, Goodwin had already been replaced by the dark entity. Goodwin—who should've been defeated by Yusei later—had been swapped in early, planning to eliminate Yusei before he could grow strong.
If Yusei died early, this world would have fallen, becoming food for the dark entity.
Rudger, too—his body had been implanted with the bone knight from another dimension, the two personalities battling for dominance, ultimately to produce a stronger threat.
Kira muttered, "So the creation of dark timelines—that's what's causing worlds to collide…"