'system?'
[ Host, there is something inside your body which provides you resilience from external influence. ]
'!?'
'Explain.' Ryuk's tone turned serious due to feeling the importance of this information, which seemed hidden from him until the end of his previous life.
He didn't blame anyone since he was engrossed in learning about this world.
[ Any external influence gets nullified the moment it tries to affect you in any way: poisons, stat debuffs, curses, mind manipulation, illusions, unauthorized access... ]
Suddenly, hearing the System's voice fading at the end point of the explanation, Ryuk's mind, which was processing everything, suddenly pulled him towards reaching a conclusion, which was not unexpected from him to begin with.