As we all know, Aokiji left the marines after a 10 day fight against Akainu at Punk Hazard. Akainu since became the Fleet Admiral but Aokiji (referred to as Kuzan from now on, since his Marine name doesn't really matter now) has been roaming the seas with his penguin whose name has been revealed as "Camel" in Volume 70's SBS. We saw Kuzan when he appeared to save Smoker from certain death, after his small face-off with DoFlamingo, who chose to walk out rather than fight, DoFlamingo said: "The man standing before me right now... What does he stand for?! Who is this Kuzan?!, Because what I'm hearing about you through the grapevine ain't pretty" Pages - Chapter 699 Page 09 & Page 10. He also goes on to tell that there is a difference between a man wandering aimlessly and a man standing firm by his convictions and that it's easy to tell the two apart. From what I guess, he knew Kuzan was standing firm by his convictions. Kuzan also said and I quote: "From the day I joined, I never held the World Government in high esteem. I can make an impact and influence matters without the veil of the Marines. They say the grass is always greener on the other side... well in my case it's actually true" Pages - Chapter 699 Page 11. Now, Kuzan could be a lone wolf, but the fact that he made a statement about being able to make an "impact" and "influence" matters without the veil of the Marines gives a hint, that he is definitely on some "side". He also spoke about the grass being greener on the other side, and the other side of the "Government" and "Marine" is non other than Revolutionaries. Note: Pirates go against the law, not against the government, it has been stated by Robin that the reason Monkey D. Dragon is the worlds most wanted criminal is because he has gone against the government. Apart from this, there aren't any other facts that I'd like to state, but from this bit it's already pretty clear in my opinion. Kuzan isn't someone who'd join the underworld or a pirate organization, but joining the Revolutionaries after having lost trust in the Government and seeing it take another step away from his belief of "justice", I'm sure he's with the Revolutionaries.