Akainu is a firm believer in Absolute Justice, and is ruthless in his maintenance of it. He has a stern, dead-serious disposition, grim, expressionless, and his the most ruthlessness of all three Admirals.
Akainu's beliefs led him to go as far as destroying a refugee ship simply because of the minuscule possibility that a scholar could be hiding on board. His logic is that if even one of the scholars of Ohara had escaped with it, the mission would've been a failure, much to the dismay of Aokiji,[4] who called him a fool for overdoing things. Akainu takes his extremist attitude as far as to kill anyone who doesn't share his point of view, as he attempted to kill Coby for his plead to stop the war. Additionally, he has no tolerance for Marines who desert their posts and even appeals of wanting to return to families instead of dying does not sway his sympathy, the only consolation he does offer is that they should not dishonor their families by running away.[5] To Akainu, any marine who is not willing to fight for justice is not worthy to be called a Marine.
Despite his status as Admiral, Akainu is also known to use underhanded tactics and is willing to lie or misdirect his enemies in order to achieve Justice. So far Akainu's manipulations have been incredibly successfull such as he managed to deceive Squardo through Sengoku's master plan, or insulting Whitebeard to get Ace angry enough to stop his attempt at escape. He finds people who attempt to interfere with him as nothing more than irritating obstacles.[6] Furthermore, he seems in many ways unthreatened by older legends and comments on this when Whitebeard claims to his men not to be intimidated by Garp, while Akainu says that he and Garp are of the same generation and promptly attacks him.[7]
Prior to Sengoku making it public, Akainu is one of the few who knew that Luffy was Dragon's son. It is unknown if he has some past relationship with Dragon or if it was simply common knowledge among the high ranking Marines that Dragon is Garp's son. As such Akainu deems that Luffy's mere existence, due to being Dragon's son, is enough to be a threat to the world, and must be eliminated. In fact, Akainu's beliefs of heritage run deep enough that he declares that even if every other pirate escapes, he personally will not permit Ace or Luffy to leave the war alive due to their bloodlines, to the point of actively hunting Luffy himself even though Blackbeard is destroying Marineford. He views criminals, whether they would be pirates, or any other sort for that matter as tools to be used against each other.