Yes, of course, the man's happiness of seeing others eat, stemming from his lack of stomach
pfffthahahah, I'm sorry, I can't take this guy's face seriously. I think the premise for his heel turn is more or less okay, but it really needed several chapters to simmer over. Just winding up as the ultimate puppet-master to make one of his students continue eating is... a leap too far, though. I'm just guessing, but maybe the author had a better way of building it all up, but was unable to commit for various reasons.
Well, at any rate, looking forward to the happy ending.