Shilo's father and a widower.
Nathan fell in love with Marni, Rotti Largo's lover, and married her at least eighteen years prior to the storyline.
While pregnant with Shilo, Marni became ill. Nathan attempted to cure Marni's illness with a medicine of his creation, only to unintentionally dose her with a poison planted by Rotti Largo in revenge for her leaving him.
Marni died, and Nathan used what little time was left to perform an emergency surgery, saving Shilo's life. Rotti, however, had Nathan arrested under the charge of murdering Marni, and then 'fixed things' by offering Nathan a job that he couldn't afford to refuse: Becoming the Repoman, and putting his surgeon's skills to good use.
Marni's death left Nathan heartbroken, guilty and paranoid over Shilo's health and safety. He told Shilo, as she grew, that she had inherited a blood disease- one that had killed her mother. In fact, Shilo was healthy, and Nathan was drugging the medication he gave her for the phony disease so that Shilo wouldn't leave, wouldn't have to deal with the outside world and its miseries.
Seventeen years after Marni's death, Nathan often laments his late night duties, but a seeming multiple personality tends to take him over- That of the Repoman- leaving him a vicious killing machine as opposed to the kind hearted father he shows Shilo.
We first meet Nathan as the Repoman, in the graveyard when he rescues Shilo from the GeneCops. Nathan takes Shilo home and puts her to bed. When she wakes up, panicked over what had happened, he denies the events that took place and tells her that she was only dreaming. He encourages her to take her medicine, assuring her that she'll only have to stay inside until he's found a cure for her illness. He leaves.
Downstairs, Nathan's story is told, and he goes to the basement to take care of a new reposession victim ("Legal Assassin"). Nathan proceeds to reposess the organs, falling into his Repoman persona and jauntily lamenting about how no one appreciates the work he does ("Thankless Job"). After reposessing the organs and snapping back to his normal self, Nathan appears disturbed at his behavior.
Later on, whilst on a job for Rotti Largo, Nathan's alarm springs to life: Shilo hasn't taken her medication. He calls her to make sure that she's alright, not knowing that Shilo has ventured from the safety of the house and is currently at the Italian Renaissance Fair. Shilo convinces him that all is well, and he goes back to the reposession. He later returns home only seconds after Shilo.
Eventually, Nathan is called in Rotti Largo's office: Mag is retiring, and her eyes are now subject to reposession. Nathan refuses, and Rotti invokes his guilt over Marni's death, reminding him of why he does this job:: To keep Shilo in the dark about the Repoman. He appeals to the Repoman personality in Nathan ("Night Surgeon"), but Nathan still can't bring himself to hurt the woman who was so close to his wife. He tells Rotti to find someone else, and leaves.
Upon returning home and finding Mag in the house, talking to Shilo, he becomes angry and throws her out, despite Shilo's protests ("Everyone's a Composer"). Shilo pleads with him to help Mag, showing him a magazine article that mentions the possibility of Mag's eyes being reposessed. He shoots her down, telling her that there are things in life that can't be changed ("What Chance Has A Seventeen Year-Old Girl?").Shilo fights back ("Seventeen"), demanding independance; she wants to be free, wants to grow up and go outside, and she criticizes Nathan for clinging to his grief for Marni. Nathan slaps her and she falls unconscious. While she's out, Rotti Largo calls her and leaves a message, revealing his attempt to steal Shilo away.
For his refusal to cooperate, Rotti sets his goons after Nathan. After killing them and then finding that Shilo has disappeared, Nathan, as Repoman, goes to the Genetic Opera to find her and deal with Rotti. It is there that Shilo, drawn in by Rotti, unmasks the Repoman and discovers her father beneath. She's sickened and horrified, and disowns her father after seeing what she mistakenly believes is what he did to Mag ("Let the Monster Rise").
Nathan then throws all caution to the wind and goes to kill Rotti for taking Shilo away from him. He reaches the stage only to be taken down by Luigi. Rotti, Luigi and Pavi then proceed to reveal all of Nathan's secrets to Shilo: Nathan had 'killed' Marni, and was poisoning her medication. In spite of Shilo's anger towards him, when she becomes faint, Nathan entreats the members of the audience to help her.
When Rotti demands that Shilo kill Nathan, Shilo refuses and turns the gun on Rotti. But Nathan urges her not to repeat his errors, and encourages her to go out and live a life worthy of remembering. The lights suddenly go out, Rotti steals the gun and shoots Nathan.
As he lays dying, Nathan imparts upon Shilo his love, and his desire for her to go and change the world with her new freedom ("I Didn't Know I Loved You So Much"). He dies.
The deepest aspects of Nathan's personality are shown through his interactions with Shilo.
Nathan clearly loves Shilo a great deal, but suffocates her by keeping her locked up in the house and safe from the outside world. Overprotective, Nathan tends to run to Shilo whenever he thinks there's a problem, and never allows her to have visitors. He is kind and predominantly gentle with her, but still retains a strict nature to keep her safe. He is passionate in his devotion to his daughter, and will act aggressively towards anyone and anything he believes is threatening her.
The Repoman portion of Nathan's personality is similar in the respect that, according to the dialogue, he too is obsessed with protecting Shilo (Onstage at the opera, it is the Repoman who violently threatens to kill Rotti if he touches Shilo). Unlike his true self, though, the Repoman takes great pleasure in making others suffer, grinning in the faces of his victims and taking sadistic amusement in their terror.
Nathan was head-over-heels in love with Marni. His utter ruin after her death is an indication that they were very close. After her death, Nathan turned his house into a living memorial for Marni, even going so far as to dress up her dead body and keep it behind a window for viewing.
Initially, Shilo and Nathan don't seem to have many serious problems with one another: Nathan is devoted to Shilo, willing to make just about any compromise for her. Shilo, on the other hand, is torn between affection for her father and bitterness towards him for keeping her caged.
At first, there doesn't seem to be any real hatred or animosity between Nathan and Rotti. Nathan is unaware that Rotti arranged Marni's death, and Rotti gloats over the power he has over Nathan. Nathan is, at the very least, tolerant of Rotti and the business of reposession, though this may only be out of necessity. Upon learning that Rotti has been conspiring to steal Shilo from him, Nathan becomes enraged with hatred, and vows to kill Rotti.
Given that Mag was Marni's best friend and Nathan was Marni's husband, it is likely that they were friendly at some point. In "Everyone's a Composer", Nathan and Mag greet each other by their first names, suggesting familiarity with one another. Though he becomes agitated with Mag for trying to get him to let Shilo out, Nathan cannot bring himself to reposess Mag's eyes when ordered by Rotti, and he seems to be upset, or at least shaken, upon seeing Mag dead at the opera.
"Everyone's a Composer"
"What Chance Has a Seventeen Year-Old Girl?"
"Tonight We Are Betrayed"
"At the Opera Tonight"
"Let the Monster Rise"
"I Didn't Know I'd Love You So Much"