I have some theories, what if that man inside iruma's ring is actually the former demon king (or his remaining fragments) and will regain his power back everytime iruma leveled up since his name is basically former demon king's name in backwards? That ring is basically waiting the right owner and guide iruma to become the demon king
Also, what if it's the former demon king's last wish before his disappearance to gramps (since he's formerly a faithful servant of his majesty) to find, flourish the next demon king, and stop that one traitor among 13 patron?
What if Iruma's parents actually are not real and just his majesty's puppets to train Iruma? You know... to seize his greed, make him feel the hardships so when the time comes Iruma wouldn't yield anything and always put others first? This one's a stretch but WHAT IF
You know the surviving test arc where they collect herbs and moster to get points, when iruma was trapped and said "because I'm a human" ali-san replied "well, not really tho", that got my imagination WILD
What if he's an illegitimate child of former demon king with a human? Or about how his blood have powerful healing power is actually an inheritance/have something to do with his birth like his wild girl best friend's and his archer teacher's and not because he's (was) a human? Ahahaha I sure take this manga a little too seriously
Bottomless greed? Lol he's just hungry and issa food lover