"Now then... Why did you betray us? This is easy; you never created Undertaker to save Japan or the marginalized. Your real goal was that woman trapped in that sphere."
Yuki was right; Gai couldn't care less about Japan and the marginalized. The only reason he created Undertaker was for Mana. However, Gai had used lies to gather everyone, hoping to save the marginalized. After all, there weren't many crazy enough to follow him just for a woman. That's why he used the marginalized and Japan's independence to bring everyone together; several had lost their families due to GHQ.
"Finding Inori was just the beginning of your plans and also the perfect sacrifice. But... Your plans fell apart from the day Inori called me. Tell me, Gai... Was the Void Genome for your use, or was it for someone else?"
This had always bothered Yuki. Gai had claimed that the King's power was meant for him. But if that were the case, why did Inori have to steal the Void Genome? The chances of success would have been higher if he participated in person, yet he didn't.
"No, the Void wasn't for you; it was for Shu Ouma. Your body couldn't handle the burden of the King's power, and finding someone who could was very difficult. Fortunately for you, Shu Ouma met the requirements. How could you not know? After all, he is Mana Ouma's younger brother, our dear 'Eva.' That's why you planned to send Inori to him. You knew Shu was a fan of Inori, and by bringing them together, your objectives would be fulfilled."
As Yuki said, Gai had never considered using the power for himself. He knew his body; it was sick and incompatible with the Void Genome. Using it would be courting death. However, Gai knew Shu, the perfect candidate. Shu was, after all, the Adam chosen by Mana, and the Void Genome was designed for his use. Gai was aware of this, having lived a part of his life with the Ouma family. He knew that Mana loved her brother passionately.
"Too bad for you, Inori entrusted me with that power. That's why you were surprised when you found out I was the 'King.' Even though you tried to revert to the original plan, you couldn't. 'Eva' didn't want anyone but her brother. Seeing your plans fail, you chose to betray us. You alone didn't have the strength to kill me, so you sought the only person who could... Yuu. However, you were afraid Yuu might fail. That's why you used the Leukocyte to kill me, under the guise of calling for reinforcements. But once again, you failed."
Gai's move had been unexpected for Yuki. Gai had used his own life as a bargaining chip to kill Yuki back then. Initially, Yuki doubted Segai; after all, if he died in that explosion, Gai would die too. However, his doubts vanished when he met Yuu. Yuu appearing at that moment when Yuki stopped the Leukocyte's attack wasn't a mere coincidence. No, he was there to save Gai. With his abilities, that was possible. They severely underestimated Yuki's power since he alone could stop and survive that explosion.
"The King's power still resided in my body, but with me alive and well, another thing worried you... That your father and Yuu would break their promise. That's why you decided to preemptively steal the Apocalypse Stone. With it in your possession, you wouldn't fear that Yuu and your father would break their promise. Too bad, once again, you failed. Next time, make sure to have a good family relationship."
The relationship between Gai and Shuichiro was very murky. Shuichiro didn't trust Gai, and Gai didn't trust him either. Their alliance was based on their nearly similar objectives. Yuki took advantage of this fragile alliance, leaking information through Segai about Gai's plans to steal the Apocalypse Stone. It was a success; apparently, Shuichiro trusted Segai more than his own adopted son. Without hesitation, he stole the stone before Gai could.
"You knew you were screwed when the plan to steal the Apocalypse Stone didn't work. Again, you failed. Yuu and your father had sidelined you. Instead of relying on a variable like you, they decided to bet everything on Shu."
This was also one of the reasons Yuki asked Arisa to make two golden tickets. He wanted to ensure with his own eyes that Shu received the King's power, and the trip to Oshima was the perfect opportunity. Although Shu was innocent in all this, his past was darker than Yuki expected. Without Rasiel, Yuki was forced to resort to his old habits from his previous life.
"You became desperate, using everything you had for a second attempt to take the stone. Even though you knew it was a trap, you still jumped into it. Tell me, Gai, is it really necessary to go this far just for her?"
Betraying your people for a woman—Yuki didn't know if what Gai felt was love or pure obsession. Love isn't wrong, but it becomes a sin when your love causes harm to the people around you. Although Yuki didn't judge him for this, he knew well that love hurts and is blind. Yuki even destroyed half of Tokyo for Inori's love, so he wasn't in a position to judge, but there was a difference. Yuki wouldn't betray his own for love.
"What do you know about me?! If I go too far?! Do you know what Mana means to me?! Do you even know?! Don't make me laugh! What does a monster like you know about love?! You know nothing! I just... Wanted... to be with her again."
With clenched fists and tears in his eyes, Gai's mind broke. After sacrificing so much for this, he felt like the most cursed of cockroaches, all just to be with Mana again. He had killed, betrayed, feeling like the most cursed creature, all just to be with Mana. Even if it meant being in the afterlife, Gai wanted to be with Mana. However, he also wished for all this destruction of humanity to end. So dying with Mana was the solution.
Yuki sighed; he sympathized with Gai's situation.
"I understand, Gai. There's one thing, though, that I won't forgive you for."
With darkness covering his face, Yuki was furious. Although Gai did everything for the love of a woman, and Yuki sympathized, Gai had touched his bottom line. So, materializing his spark gun, Yuki aimed it at Gai.
"Inori... I won't forgive you for using her as a sacrifice. So please... Die."
*Bang
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TN : mmm still sleepy