Even though Dong Tianyu knew what the best sustenance for the Hundred Ghosts Banner was, he never used it on others when he was in China.
Just as most Chinese people, when old, would yearn to return to their roots no matter where they are, sending someone into the Hundred Ghosts Banner would indeed grant them a form of eternal life. However, the ultimate fate would still be the destruction of the soul, dissipating into nothingness.
So whether one calls Dong Tianyu sentimental or hypocritical, although he would kill, he never sent anyone into the Hundred Ghosts Banner to enslave them for all eternity.
However, Dong Tianyu had a strong sense of racial pride. Deep in his subconscious, he always considered the Traditional Chinese first, other minorities in China second, and foreigners were not even within the scope of his consideration.
