Luigi Largo is Rotti Largo's eldest son, born 2019, an abusive homicidal sociopath. He wields a knife at all times and is usually wearing an ascot.
Luigi is first shown in Rotti's office, as Rotti receives the incriminating photos of his children. He appears ashamed when Rotti sees his picture and is disgusted with him.
Later on, Luigi appears in a lab with his siblings and several GenTerns. When Amber asks after Rotti, Luigi attempts to assert himself, only to end up kneed in the groin. He snaps at Pavi when he makes a lewd joke, and the pair begin to argue over which of them will inherit GeneCo when Rotti dies ("Mark It Up").
Luigi and his siblings are later seen at the Italian Renaissance Fair. Luigi is upset over not having his coffee, and lashes out at several people. When one finally delivers his coffee, he finds that they've given him decaf, and proceeds to stab the assistant in question with his knife. He finally stops when Blind Mag intervenes.
Luigi jumps into the middle of Amber's verbal assault on Mag, and the debate over who will inherit GeneCo resumes, all three siblings falling into it. They desist only when Rotti arrives and orders them all away. Luigi and Pavi are later seen at the ribbon-cutting ceremony, and are there when Amber is a no-show.
Luigi is next seen in his father's office again, when Nathan Wallace, the Repoman, is called in to receive his next assignment: The reposession of Mag's eyes. He, his brother, sister and father all order Nathan to do the job. When Nathan hesitates, Rotti, Luigi, Pavi and a group of GenTerns draw out the Repoman in him ("Night Surgeon").
That night, Luigi is present at the Genetic Opera, arriving in a flashy manner along with his brother and father ("We Started This Opera Shit" and "Buon Giorno"). During Amber's performance, he is seated in the audience, and steals his neighbor's popcorn. During Mag's performance, he's seen offstage with Pavi, playing with some of the fake snow. After Mag's fall and Nathan's arrival onstage, Luigi attacks Nathan with his knife and brings him down.
As the audience watches and Nathan bleeds out, Luigi, Pavi and Rotti expose Nathan's deep, dark secrets to Shilo Wallace. When Rotti first tells Shilo to kill Nathan, Luigi shouts an agreement; however, when Rotti then adds that he will leave her GeneCo if she does so, Luigi panics and joins Pavi onstage as they plead with their father to reconsider.
After Rotti succumbs to his terminal illness and dies, Luigi is seen with Amber and Pavi as Amber announces her appointment as head of GeneCo. Luigi applauds Amber, and becomes enraged when he doesn't hear the reporters clapping as well, threatening to kill them all before breaking out into tears over his father.
Luigi demonstrates a very unstable personality throughout the story. He is exceedingly violent, unafraid to lash out physically or verbally with others. He seems to take a macabre pleasure in blood and gore, given his reaction to Nathan in "Night Surgeon". At the end- it could be debated if his tears were real or not- he does cry over Rotti.