The prisoner approached Han Sen. Although he walked slowly, he was already very close to them. A second later, he was directly behind Han Sen.
As the prisoner walked, his cuffs clinked and clanked. When he came to a stop behind Han Sen, he fell completely silent. Han Sen couldn't even hear the prisoner breathing or his heart beating. It was as if he no longer existed.
Han Sen used his Dongxuan Aura to scan the prisoner, but he was shocked to find that he could no longer detect the prisoner's presence. Goosebumps flared across Han Sen's body.
The prisoner was standing directly behind him, but he could not feel the strange, chained man. His inability to detect the creature deeply unsettled Han Sen. He wanted to just run away as fast as he could. But he was currently casting the red bird spell; if he left his position, then the Four Symbols Seal would break. If any of the four tried to run, they'd all end up dead.