Jack was a little confused by Kira's suggestion. To be honest, he and Bommer were not particularly familiar with each other. He only knew that Bommer had become a Dark Signer because he believed Godwin had sacrificed the people of his hometown, and later discovered that it had actually been the Earthbound Immortals, not Godwin, who had sacrificed them.
Later, Kira had beaten up the Lord of the Underworld and brought several Dark Signers who had originally died back to life, Bommer among them.
But that was all Jack knew. He had never had much contact with Bommer.
Kira did not explain further. In truth, the opportunity for Jack's evolution did not lie with Bommer himself, but was hidden in Bommer's hometown.
That had also happened in the WRGP arc of the anime. It turned out the Earthbound Immortals were not limited to the few the Signers had defeated during the Dark Signer Arc. The truly strongest Earthbound Immortal was known as the "Red Lotus Demon," possessing terrifying power beyond anything the other Earthbound Immortals could match. It simply had not awakened during the previous battles of the Dark Signer Arc.
Legend said that ten thousand years ago, the strongest Earthbound Immortal had ravaged the land. At the time, a Signer from ten thousand years ago who possessed the power of Burning Soul defeated it and sealed the Red Lotus Demon deep underground. The legend of the Red Lotus Demon had thus endured for ten thousand years.
The anime later revealed that the modern Jack Atlas was the successor of that ancient Burning Soul Hero. Jack awakened Burning Soul, absorbed the power of the Red Lotus Earthbound Immortal, and made it his own, allowing his Red Dragon Archfiend to evolve into "Red Nova Dragon," his Strongest Ace Monster in the