The Seventh and eighth soul (brother of Frisk Reader)

When Frisk and her twin brother Y/N fall into the Underground as infants, the monsters who find them never expect the impact the children will one day have.
Raised lovingly by Toriel, the two grow up sheltered in the Ruins, unaware that their arrival has already shifted the balance of the world below.

As the years pass, Frisk becomes curious-drawn to a mysterious sealed door and the young skeleton on the other side named Sans. Their secret friendship blooms quietly, a flicker of light in the dark.
But where Frisk finds warmth and connection, Y/N feels something stirring within himself-a faint orange glow deep inside his chest, the Soul of Bravery that he doesn't yet understand.