The unfamiliar man before him stirred ripples in the "younger brother's" heart, which had been as still as stagnant water. He wanted to find out whether this man could really see him.
Sōsuke Aizen was the man's name.
He talked with Tanjiro Kamado until late into the night. Only well past midnight, when Tanjiro Kamado grew overwhelmingly sleepy, did Tanjiro say good night and go to sleep.
The "younger brother" silently watched the man, but he made no move. Disappointed, the "younger brother" concluded that what had happened earlier must have been his imagination.
Sōsuke Aizen suddenly spoke. "Is there something you want to say to me?"
The "younger brother" asked in astonishment, "You can see me?"
Sōsuke Aizen smiled gently. "Why would you ask that? Although having two different souls is certainly surprising, you are simply the unusual one of the two."
The "younger brother" asked in wonder, as though he had uncovered some earth-shattering secret, "Are there other beings like me in this world?"
Sōsuke Aizen explained calmly, "Everyone has two sides within their heart: positive and negative, white and black, light and darkness. Usually, the greater side becomes the personality and soul that occupies the body, while the lesser side is concealed within it, becoming an appendage. In other words, Tanjiro Kamado is the primary personality born from the positive side, while you are the secondary personality derived from the negative side.
"Normally, once the primary personality forms, the secondary personality should be unable to emerge. You should not exist, yet you were born nonetheless. How surprising. The positive side is pure, flawless white, yet the negative side is the deepest, darkest black-and the strength of your negative side is no less than that of the positive."
"Is that so? I shouldn't exist..."
At Sōsuke Aizen's words,