Sejanus Plinth was a Capitol citizen, formerly from District 2 who was the mentor of the male tribute of District 2, Marcus during the 10th Hunger Games. He was one of the 24 top-performing seniors of the Academy selected for a mentor role. He was a former close friend of Coriolanus Snow, who both referred to one another as close brothers.
Sejanus was born into the Plinth family, as the only child of Strabo and Mrs. Plinth, both of whom were wealthy District 2 residents. His father, Strabo made much of his wealth off of munitions and weapon manufacturing. At a young age, he attended school, with one of his classmates being Marcus, his future mentee for the Hunger Games. One day, Sejanus smashed his finger in the door accidentally. Marcus, upon seeing this automatically went and scooped up a cup of snow in the windowsill to help bring down the swelling. His father trained him to properly shoot with a gun every week with mandatory practise, considering it apart of the family business.
During the First Rebellion, Strabo profited off largely from the war, as when District 13 rebelled, much of the country's weapon and military manufacturing landed into the Plinth family's work. His father's decision to side with the Capitol during the rebellion and their newfound wealth eventually gave the family citizenship in the city to enjoy privileges that the most oldest and powerful families had earned over generations.
Sejanus arrived to the Capitol 10 years prior to the 10th Hunger Games, enrolled in a elementary school at 8 years of age. When word got out that he came from the districts, he was bullied and teased by his classmates who wanted to make his life a living hell. Snow thought of also participating with the bullying directed toward Sejanus, however abstained and instead opted to ignore him instead.
His father's generous donations in the reconstruction effort after the war also landed him a position at the Academy as per his request. Eventually Professor Sickle made Sejanus one of her star pupils and assistant, and regularly calls him day or night whenever she needed help.
On the reaping day festivities for the 10th Hunger Games, Sejanus was tasked by Agrippina Sickle as her aid to carry around an ornamental shield that she was awarded by successfully overseeing the bombing drills during the rebellion. Sejanus was wearing a soft charcoal grey suit with a white shirt and a paisley tie that Snow noticed almost immediately. Snow and Sejanus then exchanged pleasantries as Agrippina and Satyria were occupied discussing the deployment of peacekeepers to District 12. Sejanus then informed Snow that his family was moving to the Corso, as many owners including the Dolittles would be unable to afford the new taxes that the Capitol was about to implement to help fund reconstruction projects to rebuild the city. This worried Snow so much so that Sejanus noticed something was off and asked Snow if he was alright.
Sejanus and Snow then attended the announcement of the students who were to be mentors for the Hunger Games by Dean Casca Highbottom. Sejanus responded with his assignment of the District 2 male with misery, failing to conceal his emotions. He hypothesised that his father personally requested the assignment himself through bribes.
Sejanus first appeared at the Capitol Zoo at sunset, the day the tributes arrived, shortly after Snow was revealed with the tributes in the cage. He bought a large backpack overflowing with sandwiches and fresh plums made from his mother and attempted the help feed the tributes, who instead responded with uneasiness out of distrust. Sejanus bought out his arms through the bars, and attempted the coax Dill, the District 11 female tribute to take his sandwich that he was offering. When he caught sight of Snow, his face brightened and he waved him over. A little girl then came up to the pair and stated that he should abstain from feeding animals, referring to the tributes, which was met with disagreement from Sejanus who argued that they were kids, like him and the girl. The girl responded with further disdain. Sejanus then proposed that Snow can instead convince his tribute, Lucy Gray Baird to take his sandwich which he believed may cause the other tributes to follow suit. Snow then offered Lucy the sandwich who then proceeded to invite Jessup, the District 12 male over. Jessup then toke a plum from Sejanus and walked off without a word. Suddenly, the other tributes rushed to the fence and within a minute, all the tributes had emptied Sejanus' bag, with the exception of Marcus who stared back at him at the back of the cage with his arms folded. The news team then tried to engage with him, however he brushed them off and disappeared into the crowd.
As Snow left, Sejanus thanked him for stepping up, having hid behind a large boulder when Lucy was singing at the zoo. He reveals that he believed none of their other classmates were going to help him with the exception of Snow, and that ever since the reaping he kept thinking that he could have been one of the tributes reaped. He also revealed that his family is widely known back in District 2 and widely despised, citing that as a reason for Marcus' hatred toward him. When Snow expressed his strong belief that Marcus may win the games, Sejanus proposed that they could swap tributes, showing excitement at the prospect, springing to his feet. However, Snow turned down the proposal.
Sejanus was disappointed and apologises for making things hard for Snow, and blurts out how absurd he thinks the games are, putting kids in an arena to kill each other, believing it unnatural as animals and humans always protect their young. His distress bought him tears, saying that he doesn't want to be apart of it.
In the morning, the mentors were all required to attend a seminar led by Professor Crispus Demigloss, their old history professor to help brainstorm ideas to better engage the Capitol citizens to watch the games. Sejanus' hand went up directly after Professor Demigloss asked the class for proposals, questioning if the Hunger Games is the right thing to do in the first place. His statement was largely ignored. Clemensia responded to Festus' plan to make viewership a law, punishable if broken, citing that the games are cruel and gruesome, and thus people would avoid it. Sejanus used this opportunity to further question the ethicality of the games, saying that only a vicious, twisted person would watch children kill one another, believing that humans are above killing children. Livia snapped back using his District blood to argue that he is ignorant of what the Capitol had seen. Sejanus fell silent but was met with indirect support from Lysistrata. Arachne and Livia then argued with Sejanus, believing that the tributes and District citizens are below them.
As the mentors were talking to their tributes, Sejanus entreatingly spoke to Marcus, who was unresponsive. As the mentors came back from their meeting, Sejanus argued that there was practically no point in interviews, as they would be thrown into an arena to die anyway, with assent and agreement coming from his classmates.
Dr. Gaul then noticed Sejanus as the boy who fed the tributes and questions him. He responded that he felt sympathy for their starvation. Dr Gaul concluded that he was a rebel sympathiser. Sejanus argues instead that some of the tributes were 2 years of age, with the oldest being 8 when the war ended, and by this time they should just be Panem citizens, and be protected by the government as everyone else in the Capitol. He then paused, and blurts out that he should be replaced. The class audibly gasped, and Dr. Gaul refused immediately.
Sejanus went to the zoo later that day, and after Arachne and Brandy was killed, Sejanus kneeled down to the District 10 female tribute, sprinkling a handful of bread crumbs and murmuring something as a sign of respect.
Sejanus was present at the funeral of Arachne Crane, Snow first taking notice of him poking his food. Snow, not wanting Sejanus to be punished for not eating his food, instead opted to bring Sejanus' left over food back home. Sejanus was also present in the tour of the Capitol Arena with his tribute, Marcus. When the bombing went off, his tribute escaped, however he was largely uninjured. Sejanus visited Snow in the Hospital with Snow's book bag from the van and a stack of his mother's delicious meat loaf sandwiches.
Sejanus was also in the biology lab with the remaining mentors for a class with Dr. Gaul and began to traverse into a heated argument about the whereabouts of his tribute, Marcus. Sejanus then attempts to leave, but the doors were locked. He refused to sit down as per Dr. Gaul's request, only seating himself when Snow invited him over to sit next to him. His anger then led the class into agreement that the war and fighting should be over, with Livia, Lysistrata and Festus all showing some form of discontent.
When the class was dismissed, Sejanus follows Snow down the hall, attempting to convince Snow to stop rescuing him. Snow responded with sympathy then asked Sejanus if he had a guitar lying around for Lucy to use for the interviews. Sejanus revealed that he didn't have a guitar in his possession.
At the interviews, he introduced his mother to Snow who expressed her gratitude and thanks.
In a class with Dr. Gaul he expressed further sympathy for the Districts, which was met with objections from his classmates. He, however largely ignored them.
10th Hunger Games
After seeing Marcus strung up to poles with no way to defend himself at the start of the Games, Sejanus threw a chair at the screen and left, infuriated at what he has seen. 
That night, Sejanus entered the arena, and protested against the Games by holding vigil over Marcus's body. Dr. Gaul told Coriolanus that he must enter the arena and bring him back before anyone noticed. Unfortunately, while Sejanus and Coriolanus move Marcus's body away from the cameras, the tributes Mizzen, Coral, Bobbin, and Tanner found the two and attack them. Coriolanus accidentally killed Bobbin in self-defense, and, terrified, Sejanus dropped the idea of dragging Marcus's body. Both boys nearly died, but just made it past the barricade to safety. After the incident, Sejanus was very sad and did not participate much. 
For his act of entering the arena illegally, he was punished, but his father lessened the punishment to becoming a Peacekeeper in District 12 after he offered to improve the Academy laboratory. Sejanus insisted that Coriolanus also has to graduate from the Academy, and that wish is granted.When he arrived to his bunk room in District 12, he was immediately greeted by an excited Coriolanus, who also had been punished for cheating in the Games. Sejanus' mother sent him things such as baked goods and equipment during his deployment in District 12. He also bought him cash worth thousands of dollars and a picture of his old class with Marcus.
Sejanus and Snow trained together, with Sejanus showing greater skill in shooting than the other peacekeepers, believing the other members to be badly trained. They were soon assigned to the hanging of Arlo Chance for his bombing of the coal mines.
Eventually, whilst Snow met up with Lucy Gray after the brawl, Sejanus occupied himself with talking to Billy Taupe, Lucy's ex. Presumably, they discussed a rebel plot of sorts, and Sejanus instantly assisted and followed Billy's wishes, drawing out a map of the peacekeeper base. As they departed, Billy mentioned to Sejanus that they can talk again at the hob.
Sejanus then reveals to Snow that he was indeed planning a rebel plot with local rebels to flee to the north to escape Capitol influence, confirming Snow's previous suspicions. Unbeknown to Sejanus however, Snow used one of the jabberjays to record him which was then sent to the Capitol.
During a performance at the Hob, Snow stumbled upon Sejanus, Billy and Spruce at a shed with a sack of weapons finalising their rebel plot. Suddenly, Mayfair Lipp, the daughter of then mayor of District 12 stumbled upon the scene and threatened to out all of the rebels out to her father. In the altercation that followed, Mayfair was shot dead by Snow and Billy was killed by Spruce.
Despite Coriolanus‘ best efforts to stop Sejanus from getting into trouble, Sejanus’ rebel sympathy and loathing of the Capitol clouded his judgement. Even though Coriolanus thought Dr. Gaul would not have checked the jabberjay recordings, he was wrong as she had. He had also not considered that Sejanus was now an adult and it was too late for Strabo Plinth to buy his son out of the situation. Despite being present at Mayfair and Spruce's murder, it was the jabberjay recording which led Sejanus to be arrested, and later executed by hanging at the hanging tree. His last words he cried out were to his mother.
Sejanus is described as having soulful brown eyes, and a tall, angular frame. 
- "We're so glad that Sejanus has such a good friend"
- ―Mrs. Plinth showing gratitude toward Coriolanus Snow
Due to the fact that Snow abstained from bullying Sejanus, he held a higher standard and trust for Snow, expressing that Snow was more likely to help him than any of his classmates. Snow sacrificed and rescued Sejanus many times, assisting him breaking out of the arena and calming him down against Dr. Gaul. Despite their rather favourable relationship, Snow was two-faced, showing dissent against Sejanus due to him coming from the Districts, personally getting angry when Sejanus expressed sympathy for the Districts in front of the class.
Their relationship continued to develop positively well into their peacekeeping deployment, even calling themselves brothers, with Sejanus continuing to descend more so with the rebels. However, he was betrayed by Snow who recorded Sejanus's rebel plans. His actions led to Sejanus' execution and death. After his death, Snow was convinced he had no choice, and trespassed into Sejanus' locker, where he ate a cookie. He then proceeded to cry and vomit.  Afterwards, Snow kept Sejanus' real cause of death a secret, and successfully become an heir to the Plinth family.
- "Sejanus hasn't come home. I'm so worried"
- ―Mrs. Plinth expressing her distress at the disapearence of Sejanus
Mrs. Plinth was caring toward Sejanus, showing gratitude to Snow for being kind to him. Most of the time, she cooked and baked food for Sejanus and to an extent, his friends and allies including his peacekeeper squad. She cried out of distress and worry when Sejanus hadn't come home when the games began, displaying her loving nature toward Sejanus.
After his death, Mrs. Plinth was left devastated. Strabo expressed that she needed something to live for.
- "My wife needs something to live for. So do I for that matter"
- ―Strabo Plinth revealing to Snow his grief after Sejanus' death
Strabo had a strained relationship with his son, Sejanus, however did show some degree of kindness and care for him. In fact, Mrs. Plinth revealed that the only reason why Strabo decided to reside in the Capitol was because he personally believed it would give his son and grandchildren a better life. However, he largely misunderstood Sejanus, who would rather live back in District 2. Strabo resorted to bribes and corruption to give Sejanus the best opportunity, as a mentor and a spot at the academy. Despite his best attempts, Strabo tried to make Sejanus get more in line with those from the Capitol, believing it best for him which was met with dissent from Sejanus. Although their relationship was strained, Strabo showed distress and grief after his son's death, getting Snow as his heir to fill the hole of his son to get another reason to live for.
- "It's the compassionate one. Where's your tribute boy? Any clue?"
- ―Dr. Gaul taunting Sejanus about Marcus
Dr. Gaul and Sejanus disliked one another, with Dr. Gaul taunting him constantly, referring to him at the compassionate one, boy and the Plinth's brat, avoiding using his real name. They disagreed regularly, however Dr. Gaul believed that Sejanus' compassion was a rather good trait. Nevertheless, their disagreements of the Districts led to arguments, as Dr. Gaul disliked the Districts greatly, and Sejanus believing that the Districts and the Capitol should reunite. He also showed disobedience to Dr. Gaul, disrespecting her and refusing to adhere to her requests.
Dr. Gaul didn't care for Sejanus at all, showing no sympathy for his death, and only helped save Sejanus from the arena only due to the effects that is may have on the Capitol, not because his life was in danger.
- "Marcus, this is for you"
- ―Sejanus trying to feed Marcus, who only ignores him
In District 2, when they were young Marcus showed some form of kindness toward Sejanus, helping him when he broke his finger. However, when he left for the Capitol, Sejanus was disliked by Marcus alongside much of the District. Marcus resented Sejanus during much of the mentorship program before the games, ignoring him. Despite Sejanus' best efforts, Marcus never talked back to him. 
When Marcus was shown in the Capitol arena hanging and badly beaten, Sejanus showed a extreme emotional response, showing the sympathy and care he felt for Marcus. Despite their unfavourable relationship, Sejanus still attempted to make amends and help Marcus.
- Sejanus was disliked in the districts for having relations to the Capitol and disliked in the Capitol for being from the Districts.
- Sejanus wanted to be a medic instead of a Peacekeeper, and he disliked the idea of violence.
Notes and references
- Canfield, David (January 21, 2020). Who's the star of the Hunger Games prequel? Read the exclusive first excerpt. Entertainment Weekly. Retrieved on January 26, 2020.
- The Ballad of Songbirds and Snakes, Chapter 5
- The Ballad of Songbirds and Snakes, Chapter 23
- The Ballad of Songbirds and Snakes, Chapter 1
- The Ballad of Songbirds and Snakes, Chapter 2
- The Ballad of Songbirds and Snakes, Chapter 6
- The Ballad of Songbirds and Snakes, Chapter 7
- The Ballad of Songbirds and Snakes, Chapter 9
- The Ballad of Songbirds and Snakes, Chapter 10
- The Ballad of Songbirds and Snakes, Chapter 11
- The Ballad of Songbirds and Snakes, Chapter 12
- The Ballad of Songbirds and Snakes, Chapter 14
- The Ballad of Songbirds and Snakes, Chapter 15
- The Ballad of Songbirds and Snakes, Chapter 22
- The Ballad of Songbirds and Snakes, Chapter 25
- The Ballad of Songbirds and Snakes, Chapter 24
- The Ballad of Songbirds and Snakes, Chapter 27
- The Ballad of Songbirds and Snakes, Chapter 28
- The Ballad of Songbirds and Snakes, Chapter 29
- The Ballad of Songbirds and Snakes, Chapter Epilogue