Inoue Mari is the de facto leader of the Marked for Death party. She is a missing-nin jounin from the Kirigakure, having abandoned a mission to invade the land of Noodle at the beginning of the story to attempt to help Shikigami found a new village in the Swamp of Death in the northwestern corner of the Land of Fire.
Mari is a seduction and infiltration specialist, with top-tier social skills and genjutsu abilities as well as strong close-quarter combat skills(taijustu). She is also a taijustu champion, although that may be achieved through cheating. She's good at dancing, can sing well, but only a passable flower-arranger, but is a bad cook.
Mariko is raised as a future innkeeper. When not training for this purpose, she spends time with her friends and family, notably her uncle, Kazuhiro. When she returns home one day, she discovers her mother speaking with a Mist recruiter. Eavesdropping on the conversation, she hears the recruiter explaining that Mari could become a ninja, and her mother offering token objections before accepting, moving the family to Mist.
Mariko changes her name to Mari, both considering her old name too girly, and out of frustration with how she's treated by the boys in her class. Kazuhiro comforts her, suggesting she find a way to stand out as a ninja. After much thought, she decides to improve in Taijutsu, manipulating an older ninja into giving her lessons.
Some time shortly thereafter, Kazuhiro sexually assaults Mari. She attempts to tell her mother, who slaps her and tells her off for lying, warning her not to make such claims again.
Her taijutsu instructor dies an indeterminate amount of time later, leaving her assigned to Usami, an infiltration specialist. Usami complains that her chakra control and social skills are wasted in Taijutsu. After something Usami says remind her of Kazuhiro, she freezes up; recognizing the signs of trauma, Usami changes the topic, explaining the benefits of genjutsu and infiltration before dismissing her for the day. Before Mari leaves, Usami offers a piece of wisdom: “A ninja does not have enemies. All they have are bodies that haven’t been disposed of yet.”
After training under Usami's tutelage, Mari takes the lead role in a seduction mission. Accommodating her history, Usami changes the plan to target Lord Uesugi's head maid instead of the man himself. The mission is successful. Knowing that she'll have to kill the maid, Mari refuses to strangle her, despite that being the standard procedure. Unwilling to let her suffer, Mari stabs her through the heart, killing her almost instantly.
Usami congratulates her on her success, ruffling her hair and noting that the first seduction mission is always more difficult than you'd expect. Mari asks if he'll recommend her for the chūnin exam. Usami refuses, saying that although she has the talent of a chūnin, she lacks resolve, being unable to kill her feelings while she's on a mission.
Mari spends a month preparing, assembling allies, before returning to her home. There, she convinces Kazuhiro to come with her, luring him to an isolated location before turning every torture and genjutsu she had against him, concluding with a technique she'd designed specifically for him, to make him feel everything he'd ever made her feel. The technique forced his heart to give out. Her mission complete, she disposed of his body, using her connections to make sure he wouldn't ever be found.
Jōnin: Pre-Hidden Swamp Edit
Mari (now Inoue-sensei to her youngers) occasionally saw Hazō when she was visiting his team leader, routinely taking the opportunity to tease him and ruffle his hair.
She was involved in Shikigami's plan to form a new village by claiming they were sent on a suicide mission.
Hidden Swamp Edit
Inoue was impressed by Hazō's team's execution of a killer alligator, eagerly demanding details. Expressing pride in the team, she then listened to the remainder of their report, before telling them to leave some aspects out at the later meeting. After Hazō asked how the other teams had done, Inoue filled them in, before dismissing Hazō and Wakahisa to speak with Keiko in private.
Later, she had Keiko pass on a message to the two, letting them know that "if [they] ever feel like [they]'re breaking, go talk to her. She can help."
After the team's next mission, Inoue put them through genjutsu training, simulating an attack on Hidden Swamp by Zabuza. In response to Noburi's complaints about the genjutsu's difficulty, she replied that she's produced genjutsu terrifying enough to stop hearts, and that if this was too much, they would never be able to stand up to a real genjutsu attack.
Slightly more than two weeks after the group's first entry to Hidden Swamp, Inoue detonated an explosive seal, making use of judicious amounts of sealed blood and her headband to fake her own death. When Hazō's team came to investigate, she put them under a special genjutsu, Truth Lost In The Fog, to try to convince them to leave Hidden Swamp with her. She said they also had the options of giving themselves up to Zabuza, or rebelling against Shikigami, or sticking with him to the end, saying that no matter what they chose, she wouldn't hurt them. Hazō voted to stay, but noted that he'll go with the majority choice. Keiko voted to leave. In response to Wakahisa's question about why Inoue was only leaving then, she told them that they'd planned around an imminent war, and with it not happening, and Jiraiya showing up in the area, it was too dangerous. After further discussion of the details, Wakahisa voted to leave, and Hazō followed the consensus. The decision made, Inoue began preparing the area to fake the team's deaths. 
For their first lesson, Inoue asked the team where they should go, providing relevant information about the Elemental Nations. After some analysis, they chose Iron, and she agreed that it was a good choice. On the way to Iron, she tested them periodically on awareness, ability to henge, and other skills. Once they arrived at a minor village, she had Hazō pretend to be the group's leader.  In this manner, they gathered information about the area, learning about the Liberator and the Black Hunter. 
After being asked too many questions, Inoue became frustrated, telling the genin to rely on their own common sense occasionally. After shooing them off, she gathered information from the local smith, before overseeing the team's hunting of lake monsters. She allowed Hazō to be attacked by chakra voles, to teach a lesson about awareness, but when she detected the Black Hunter, she told the team to retreat to the village, while she pursued, leading the Black Hunter to detonate a large explosive tag in the forest. Upon discovering that the team had followed her, she put them on punishment detail. 
[WORK IN PROGRESS]