Robin

When Julia died, three years prior to the story, on the sea after the ship she was on, the Nivose, sank, Robin met the Earl, who promised to bring Julia back to life. Julia's soul, though, was placed within Robin's body as part of the exchange, and Robin's soul was lost.

Robin/Julia later met the Exorcist, Cross, who transplanted his left arm onto Robin/Julia's body and made him/her his apprentice. When Cross left to Japan on a mission and left behind an important artifact, the blade Abaddon, Robin/Julia went after him to deliver it.

During his/her journey to find Cross, Robin/Julia was thrown off of the ship he/she was traveling on after losing his/her money and was left in Osaka, Japan. He/she was then pulled off of the street and fed by Lenalee, who worked in the restaurant Robin/Julia had collapsed in front of. In order to pay for the food he/she had eaten and upon Lenalee's suggestion, Lenalee's boss forced him/her to work as a waiter, going so far as to make Robin/Julia wear a short-skirted maid's outfit.

While working to pay off the 'debts', Lenalee found Robin/Julia's locker, urging Robin/Julia to show Lenalee the picture of his/her 'sister', Julia, in a locket he/she carries, with Lenalee explaining after that she envies Robin/Julia, as she is only half Japanese. Robin/Julia then explained the nature of Exorcists to Lenalee, and also explained why he/she came to be in Japan during his/her search for his/her master, Cross. After work, Lenalee received a letter, and her boss told Robin/Julia her background; how after her parents died, her fiancé was the only one she had. He, however, was tragically lost at sea three years prior, on the same ship Julia had died on. A month before Robin/Julia’s coming to Japan, though, Lenalee had received a letter concerning her fiancé, making Robin/Julia suspicious.

Immediately after this, the cursed scar on Robin/Julia’s eye acted up, leading to Robin/Julia following Lenalee when she rushed to the church to meet with her "fiance".

As the Earl attempted to finalize Lenalee's contract, which would place the soul of her fiancé into her body and turn them both into an Akuma, Robin/Julia intervened, revealing the Earl to Lenalee for what he really was and explaining that the only way to save the soul of Lenalee's fiancé was for her to destroy the contract herself, as Robin/Julia attempting to destroy the contract would end in the soul of Lenalee's fiancé being erased.

When Lenalee chose to become an Akuma alongside her fiancé, Robin/Julia engaged in battle with the Earl and his two minions, James and Harold, to protect her. Lenalee begged Robin/Julia not to fight for her sake, but he/she corrected her, saying that he/she does not fight out of revenge against the Earl or for Lenalee's sake, but for the sake of his/her own kind, the Akuma, revealing his/her true nature as a sealed Akuma.

As Lenalee lamented being alone in the world, Robin/Julia called her a crybaby, telling her to be strong because she was, at least, still alive. He/she continued to fight the Earl, though using his/her Anti-Akuma weapon caused the seal on his/her eye to become strained, nearly reverting Robin/Julia to their original Akuma nature. As he/she fought, Robin/Julia encouraged Lenalee to live for herself and to not rely on the idea of her fiancé coming back as an Akuma.

Then, the Abaddon, an ancient weapon Robin/Julia had come to Japan to deliver to his/her master, Cross, intervened before Robin/Julia’s Akuma nature was completely released, and as Lenalee tore up her contract to the Earl, thus releasing her fiance's soul, Robin/Julia defeated the Earl's minion Akuma with Abaddon.

The Earl then fled, goading Robin/Julia to pursue him to continue fighting his Akuma and to witness the end of the world.

Robin/Julia left Lenalee with the locket that had held the picture of Robin and Julia inside, and went off to find Cross. As he/she did, he/she lamented the crack that Abaddon had gained in the blade from the fight with the Akuma, fearing punishment from Cross.