Blueno

Blueno a former bartender of Water 7 and later revealed to be an asassin called CP9

Personality
While the entire Water 7 CP9 unit gives the first expression of emotionless justice-devoted killing machines, Blueno is the only one to maintain such a façade. While the others- Kaku, Lucci, Kalifa, Jyabura, Fukurou, and Kumadori- are shown taking pleasure in fighting, toying with their opponents and so on, Blueno remains calm and collected nearly all the time. As a result, Blueno comes to symbolize the cynical, evil actions of the World Government - namely using Nico Robin, blackmailing her through traumas inflicted by the World Government in the first place.

Rokushiki
Blueno's Tekkai seems to be the one of the more powerful ones of the group, and he was the first to reveal any variations of the move. However, despite this advantage, Luffy was able to use his new Gear 2 abilities to defeat him when they fought in Enies Lobby. Lucci stated that Blueno's bartender job has dulled his senses, but it might just be another show of the arrogance of most of the CP9 unit. Nevertheless, with Luffy only having recently developed his Gear Second mode around the time when he used it against Blueno for the first time in combat, Blueno has been made memorable as the first adversary to receive the honor of witnessing Gear Second's first activation, as well as the first to be subsequently felled by Luffy while in this state. Bearing a Douriki of 820, Blueno was no run-of-the-mill fighter.

Devil Fruit
Blueno ate the Doa Doa no Mi, which allows him to create doors on any surface. He has even created "air doors", doors in the air itself, which lead to what seems to be another dimension. Blueno is also able to create doors on people, and did so to Luffy's face, causing it to spin like a revolving door. In battle, Blueno also uses his door to move freely through the entire environment, setting himself up for sneak attacks, and even creating small doors wherein he traps his opponents' feet.

History
When we first meet him, he is seen as a bartender in Water 7 and seems to be the most friendly with Franky and Paulie, talking with them about life and their current activites.

He soon shows his true nature when he, along with the rest of CP9, attacks Paulie and Iceburg for the Pluton blueprints. He is the agent that Robin ran into on the streets in Water 7 while she was with Chopper, as well as the agent whose Devil Fruit powers were used in both attempted assassinations of Iceburg. His power was also vital in thwarting Sanji, Franky and Usopp's attempt to rescue Nico Robin on the Sea Trains.

However during the debriefing when the Straw Hats invade Enies Lobby, he notices Spandam's phone off the hook and realizes something amiss. His instincts prove right as he meets Luffy on the roof of the Courthouse of Justice and fights against him. Unlike their last encounter on Water 7, Luffy manages to break through his Tekkai as well as figure out the "soru" move to fight him evenly. Not only that, Luffy reveals his new Gear 2 technique to him, literally pounding the CP9 agent around the roof. After a bit more fighting Luffy goes to finish him a Jet Bazooka, rather then dodge Blueno decide to take it head on with his strongest Tekkai which he manages to stay on his feet after the impact. Luffy then is about to show his Gear 3rd technique to him but Blueno collapses shortly there after, having been knocked out from the Gear 2nd move before in a delayed reaction.

After the Buster Call left Enies Lobby in ruins, Blueno turned out to be the savior of CP9, using his Air Door to protect them from the annihilation of the island by the Marine onslaught. Most of them had survived through their fights against the Straw Hats despite their injuries, except for Rob Lucci. Their leader had sustained so much damage from his battle with Luffy that he was in need of some serious medical attention. He and Jyabura were the first to overhear Spandam's plans to capture them as scapegoats to blame for the failure of their mission, and later is seen walking along the Sea Train tracks with the others.

They reached St. Poplar and became street performers to earn medical funds for Lucci. He collected the money while Jyabura, in his full wolf form, thrilled audiences by jumping through hoops of fire. After paying for Lucci's medical treatment, he sat at a café with Fukurou, Kaku, and Jyabura as they waited for Kalifa and Kumadori to return with the shopping, reading a newspaper as the others joked around. After Lucci was discharged from the hospital, he and the rest of CP9 went for a bowling match. However, the Candy Pirates invaded the town, so CP9 dealt with the pirate problem. Blueno was seen flykicking one of the pirates on the ship. While they were initially applauded by the locales for their actions against the pirates, the townspeople's view of the agents completely changed as they witnessed Lucci deal excessive justice on the defeated pirates.

Having given the residents of St. Poplar such a fearful image of themselves, the agents decided to leave the place. Just before leaving however, they were given a flower as a sign of thanks by a little girl that was taken hostage by the pirates. Taking this gift and commandeering the Candy Pirates' ship, they sailed back to their homeland. Upon arrival, they spied upon the next generation of CP9 agents being trained. As they were watching, they found out the pursuers that Spandam sent had caught up with them. In order to protect their homeland from this people, the agents dealt with them. Blueno is seen holding Very Good's head and the Den Den Mushi Lucci uses to give their former leader a message. After Lucci tells Spandam that they would come back for him someday, the agents commandeer their pursuer's ship and sailed off from their homeland. However, the now planted flower the grateful girl gave them on their homeland is seen behind the silouhette of their ship in the distance.

Trivia

 * Blueno is the first person to witness Luffy's Gear Second and also the first person to be defeated by it.
 * In the Volume 44 SBS, it was revealed that when Blueno was younger, he loved baseball.
 * He has a bull theme, due to his horn-like hairstyle. He is also referred to as a cow by Luffy numerous times.
 * When invading the Iceburg's mansion he was wearing the bear mask.
 * In a recent Weekly Shonen Jump poll to determine the most popular One Piece characters, Blueno ranked at 81st.