In Wanheda (Part 2), Titus stands next to Lexa's throne when Roan brings in a bounded Clarke as his bounty. Lexa orders her guards to arrest Roan. Titus inquires what should be done with Wanheda, but Lexa orders everyone out of the room so that she may speak with Clarke privately. Titus hesitates in leaving, but Lexa again orders him out.
In Ye Who Enter Here, Lexa enters the throne room in Polis where the representatives from the rest of the clans have gathered. All bow before her except for the Ice Nation representative. Titus confronts him and the Ice Nation representative tells him the Commander should bow before him because they don't make treaties with enemies. Titus tells him that the Commander bows before no one. Lexa switches to English in honor of the Skaikru who have yet to arrive and tells Titus to stand down. The Ice Nation rep asks why Wanheda is still alive and calls Clarke Lexa's "weakness." Titus asks about the Ice Nation army that moved in close to Polis and he excuses it as "military exercises." Indra calls him out on crossing the border of Trikru lands. Lexa calls a halt to the argument and invites the Ice Nation representative to join her to speak in private on the balcony where she has a message to deliver to Queen Nia. She kicks him off the balcony, killing him, and turns around to ask if anyone else wants to question her.
Outside Polis in the woods, Lexa is training with Aden while the other Nightbloods watch. Aden gets a hit just as Titus announces the Sky People have arrived. He orders the Nightbloods to pair up and continue training. Lexa tells him that Aden is better than she was before her Conclave. They discuss the summit and Titus warns her about antagonizing the Ice Queen by offering the Sky People a seat at the summit. He asks why she is having the Sky People join the Coalition when they are there for a treaty and the rest of the clans will not agree to it. Lexa says everyone will agree when they see Wanheda bow before her. He tells her if she wants Wanheda's power, she needs to kill Clarke.
At sundown, the summit begins with the Grounder Anthem as Clarke strides into the throne room and takes a stand before Lexa. Clarke pauses in front of Lexa before dropping down on one knee and bowing to her. Roan is the first to bow to Lexa after Clarke and the rest of the people follow suit with Kane and Abby and the rest of the Skaikru as the last kneel. Lexa orders everyone to rise and welcomes the Skaikru and Clarke to the summit. She tells the rest of the clans she is initiating them into the Coalition and the leader of the Skaikru will bear the mark. Abby passes the leadership over to Kane and he offers his forearm to be branded with the mark of the Coalition.
Octavia, Bellamy, and Pike barge in, holding a guard captive. Bellamy warns everyone the summit is a trap. Ivon, the Ice Nation representative, tells them it was the Skaikru who barged into the summit with guns. Pike says they are right because two Skaikru guards are already dead. Lexa asks how they came by the information and Octavia realizes Echo is no longer with them. Bellamy realizes Echo betrayed them as Kane tells him to stand down. Raven comes across the radio and tells them that the Grounders attacked Mount Weather and it is completely gone with only her and Sinclair surviving. Ivon tells them that is what they get for moving their people back into Mount Weather and the Ice Nation did what Lexa was too weak to do. Lexa declares war and orders the Ice Nation delegation along with Prince Roan to be arrested. Abby worries that Arkadia might be under attack next and Lexa commands them to go. Indra offers to escort them and tells Octavia she hopes she kept up on her training because she will need it before giving her back her sword. Bellamy tells Clarke they need to leave while Lexa offers Clarke protection if she remains as Skaikru ambassador. Clarke tells them she is staying to make sure Lexa keeps her word. Bellamy warns Clarke that Lexa will always put her people first and tells her to come home but Clarke apologizes and stays. Later, Titus leaves Lexa and Clarke alone in the summit room.
In Watch the Thrones, Titus stands next to Lexa's throne and orders Nia to be brought forth in chains and states she confessed to the destruction of Mount Weather. When Nia calls for a vote of no confidence, Titus orders her to be taken away but the ambassadors vote Lexa out. When Clarke doesn't vote and Nia doesn't recognize her vote, Titus reveals they took the brand and have been made the thirteenth clan, meaning the vote fails. Titus orders the ambassadors to meet the same fate as Nia but she says they won't because their armies would retaliate. Nia then challenges Lexa to fight to the death for the right to the throne in which she has to oppose Nia's son, Roan. Clarke is worried for Lexa but Lexa says that nobody fights for her.
While trying to convince Lexa not to fight directly, Clarke why Lexa has to fight when Nia doesn't while Lexa is teaching the Nightbloods. Titus explains that Lexa's strength is being questioned because of her efforts to protect Clarke's people. Titus takes the Nightbloods away so Clarke can try to convince Lexa not to fight. Clarke fails but eventually discovers Nia has been hiding a Nightblood of the Ice Nation, Ontari. Titus realizes this was want Nia wanted all along, an Ice Nation Commander and begs Lexa to chose a champion before it's too late, but she still refuses and sends him away to talk to Clarke. Titus returns to tell her it's time for the challenge to begin. Titus observes the battle between Lexa and Roan and is shocked when, after Lexa wins, she kills Nia for losing the challenge and declares Roan king.
In Bitter Harvest, Titus delivers a gift to Clarke and Lexa from the newly appointed King Roan as proof as his allegiance to the Coalition and to provide a scapegoat for bloodlust the other clans have after Skaikru massacres a peacekeeping army, Carl Emerson. Titus and Clarke both tell Lexa Emerson should die for nearly instigating a war between the clans and Titus reveals Lexa gifted her with his punishment personally. Titus later visits Clarke in her room and warns her that because of Clarke's influence, Titus fears she will get Lexa killed over Clarke's proposed new policy "blood must not have blood." Clarke sympathizes, but tells Titus she can't betray her people to protect Lexa, and Titus leaves saying they have reached an impasse. Titus later attends the ceremony expecting Emerson to die at Clarke's hand, only for Clarke to refuse. Titus tries to get Lexa to kill him instaed, but she banishes him from their lands. Titus is later revealed to have captured John Murphy to torture information out of him about Clarke and the chip he had on him.
In Thirteen, Titus continues torturing Murphy for information on the chip, Murphy tells him about A.L.I.E., Jaha, and how the world ended because of her. Titus later attends Ascension Day before Semet interrupts them because Titus promised he would be heard. When Semet reveals Skaikru attacked their village, Titus tries to convince Lexa to exterminate Skaikru in retribution. Lexa decides to summon the army of the twelve clans to blockade Skaikru inside their lands and anyone who attempts to cross it will be killed. Semet attempts to kill Lexa in rage over her decision, but Titus takes Semet's knife and kills him. Titus arranges for Clarke to transported back before the blockade before it goes into effect. After Lexa asks Clarke to stay in Polis, Titus tries to convince Lexa to let Clarke go as he sees her as a sign of weakness.
When Titus returns to check on Murphy, he discovers he escaped his bonds and is attacked by him. Titus overpowers him and Murphy relents, telling Titus more about the history of A.L.I.E. 2.0. Titus puts Murphy in Clarke's room and waits for Clarke. When Clarke arrives, Titus reveals he is going to kill Clarke with Murphy's gun to frame Skaikru and have Lexa exterminate the rest of her people so Lexa will gain back the respect of her people and be safe. In the commotion, Titus accidentally fatally shoots Lexa. Titus becomes horrified at what he has done and desperately helps Clarke try to save her. On her deathbed, Lexa makes Titus promise to never hurt Clarke again and he honors her wish. When she dies, Titus removes the Flame from Lexa's brainstem and puts it into a container.
In Stealing Fire, Titus gives Clarke and Murphy cloaks so they can escape, fulfilling his promise to Lexa. Clarke questions how he is still alive and Titus reveals he is the only Flamekeeper they have. Clarke asks to see Aden and Titus reluctantly agrees. When Ontari arrives and tries to kill Clarke, Titus stops her and lets her into the Conclave. Clarke questions Titus' decision to let her in, only for Titus to respond that it is her birthright. Titus also reveals that the Flame just deepens what is already present and if Ontari wins Azgeda will control the Coalition and wipe out Skaikru. Titus hears the horn of victory horn and rushes back to Lexa's throne. He sees Ontari on Lexa's throne holding the heads of the other Nightbloods and witnesses in horror as she declares herself the winner.
Clarke comes to see Titus to beg him not to put the Flame in Ontari, but Titus says he has to. Titus reveals that if anyone else tries to take the Flame, it will take their life. Clarke remembers that Lexa killed seven in her Conclave but there were actually eight and asks about the eighth. Titus reveals she fled, dishonoring her blood, but Lexa refused to let Titus kill her. Ontari arrives and Titus hides both Clarke and the Flame from her when she demands it. Titus sends Murphy with her to perform a purification ritual before it can be implanted. When she leaves, Titus gives Clarke her name: Luna, indoctrinates Clarke as a Flamekeeper, gives her the Flame and the journal of the First Commander, and shows her a secret way out to find Luna.
Roan delivers Titus to Ontari claiming he lost the Flame and asks where Clarke is. Titus reveals that he gave Clarke the Flame so Ontari could never ascend. Roan moves to kill him but Murphy states Titus is the only one who knows how to perform the ritual and despite Ontari's order to kill Titus, Roan realizes Murphy is right, they need Titus alive. In response, Titus slits his own throat on Roan's knife and saying "for Lexa" before falling into Ontari's bathtub and dying.