As expected, Gray wasn't under any influence but his own shortsightedness. The dude left behind a super sexy lady totally devoted to him to go after some moldy old book. That's really everything that needs to be said about his stupidity.

Gajeel is smart, though. He joined the council punitive force, which grants him two valuable things: He's legally hunting down and fighting criminals, likely the toughest ones, with the organization doing all the annoying work for him, that is, finding the targets and sorting out any damages to the surroundings. He just needs to travel there and fight. The other bonus is that he gets to fight alone, without needing to share the opponents with other battle crazy powerhouses. After all, the squad following him is made of the useless council nonames good for nothing but carrying his food and camping equipment.