Gluttony… Ren may attack him to sate his desire for EXP.
He seems to like to have a high level, and Solo Players like him generally have such tendencies.
If those feelings of desire were to reach their peak, then he would definitely attack any lone enemy.
Another possibility is Greed… The fact that he’s become a bandit leader, and is collecting treasure may come from his desire for wealth.
I want to say that I have a monopoly on Greed, but I never unlocked that series.
It may be that each weapon has a different curse it can unlock.
Last is perhaps pride.
People who believe that level is everything, and look down on those of low level are common in Net Games.
Perhaps his lone wolf-like attitude is actually a form of conceit.
No, that’s probably Itsuki.