A Record of a Mortal's Journey to Immortality: I Asked You to Draw Talismans, So How Did You Secretly Become Invincible?

After signing a contract of indenture, Lin Changyu was sent to a shady talisman factory. He spent all day and night drawing talismans, until his spiritual energy ran dry and his fingers warped.

But Lin Changyu awakened a Proficiency System.

Drawing talismans raised his proficiency, making each one easier than the last. Others drew ten a day and ended up exhausted. He could draw a hundred a day without breaking a sweat.

His trash spiritual root made it impossible to practice the Root-Nurturing Art? Proficiency could be transferred.

He poured all the proficiency he'd earned drawing talismans into the Root-Nurturing Art. His spiritual root healed day by day, and his cultivation soared.

You said he was supposed to be a forced laborer. How did he quietly become an immortal?