The Millennium Swordsman (千年の剣士 Sennen no Kenshi) is the sixteenth episode of the D.Gray-Man anime.
Allen goes with Lenalee to Rome, to find Kanda, as he had not made contact for a week during his mission. Allen, before going on the train, apologizes to Lenalee for his actions during Road's attack, apologizing for getting mad at Lenalee for saving his life.
Allen and Lenalee then get on the train where they are briefed on the mission, which states that it is possible that a swordsman from a thousand years ago was still alive and fighting in the coliseum.
Allen and Lenalee then get to town, and find out that bounty hunters are crowding the place, finding out that Claudia the daughter of a rich family, was kidnapped. They eventually head to the coliseum where level 1 akumas were. During their fight, Victorio then appears, being able to kill the Akumas. Kanda jumps down and fights with Victorio, during which Allen and Lenalee then learn from Kanda's finder, Peidro, that Victorio's sword has innocence, also Kanda was fighting him for three days straight. Kanda is able to cut through Victorio, cutting his neck, but to no avail as Victorio is able to heal automatically, allowing Victorio to cut through Kanda's gut.
It is shown that one thousand years ago, that a king in Roma had a beautiful daughter named Sandra, causing many men to come across the land to claim her hand in marriage. Sandra eventually proclaimed she will only marry the strongest man in the world, having her family's swordsman Victorio, although Victorio had never loss. Kanda is then seen at the very arena all those fights had taken place at, fighting against the same swordsman who had lived one thousand years ago.
Allen is then seen at the black order, talking about Kanda's recent assignment and finds out, from Komui, that Kanda has not contacted the black order for an entire week. Komui, knowing that there are Akumas in the area, decides to send Allen to Rome as well, to which Allen agrees. Allen is then seen at the boat, where he is surprised that Lenalee was coming as well, although she was still in a bad mood, as Allen remembered that she had became angry at him for yelling at for saving him, instead of the akuma.
Allen and Lenalee are then seen at the train station, where Allen apologizes to Lenalee. Lenalee then berates him for not letting her fight beside him, as well as believing that he is the only one who carries burden of the world because he is the only one who can see them. She then walks on the train, making Allen wonder if she had actually forgiven him.
While on the train Allen learns about the information they currently have on the mission, finding out, from Lenalee, that a roman swordsman who lived a thousand years ago was still fighting, figuring he may be an accommodator but wonders if innocence can prolong a human's life. They also find that Akumas have been appearing around the arena but none of them had ever gotten leading to Komui to believe innocence was involved. Kanda is then seen at the ring using his innocence, it is then shown that level one Akumas were destroyed.
Allen and Lenalee then arrive at the city, and find that bounty hunters are all over the city. They find out that a daughter from a wealthy family was kidnapped by the sword fighter who has been living for a thousand years.
Allen and Lenalee decide to go to the sardine family party, to try to find out something. They find out that the kidnapped girl is engaged to a viscount, who has just announced the reward will be 1/10 of the sardine fortune, making the current family head angry.
Allen and Lenalee then go through a window to speak with Claudia's father and reveals that they are with the black order, which Claudia's father seems to know. Claudia's father then tells them about Claudia and how she had seen a swordsman who kept on reporting to her, that the strongest man has yet to be found. Claudia was then kidnapped the moment she was engaged to the viscount. The Viscount then comes in and tells that if Claudia went through the marriage the Sardine family would be recognized among the high class family. Allen before leaving then berates the two for valuing money more then Claudia.
Allen and Lenalee are then seen outside upset that they didn't learn anything from them. Lenalee then talks with Allen, and seems to skeptical about Claudia supposedly running away, thinking that the swordsman may exist after all.
The next day the bounty hunters go to the coliseum, where they are bombared with bullets from level one akumas. Allen and Lenalee then go in and begin to fight off the akuma and try and help the bounty hunters to safety. It is revealed outside the coliseum that the bounty has been raised to one fifth of Sardine family fortune. Inside the coliseum Victorio appears and is able to take down the level one akumas as well as the other bounty hunters who were still in there. Allen tries to go down and fight Victorio, but Kanda stops him, claiming that he is his opponent. As Kanda went down and begins to fight Victorio Peidro, Kanda's finder, finds Lenalee and tells her and Allen about Victorio and that his sword has innocence which has been keeping him alive for a thousand years. He also tells them that Kanda and Victorio had been fighting for three days straight before the Akumas had interrupted them, causing Victorio to disappear. It is noted that the two did not use their anti Akuma weapons, possibly do to their pride as a swordsman. Kanda and Victorio's swords clash, and Kanda is able to slash Victorio in the neck. His wounds however heals immediately afterwards and Victorio cuts Kanda in the gut, causing him to bleed.