Hera unleashes her true form after warning the demigods to look away. Jason doesn't understand the warning until it's too late and sees Hera's true form, which kills all the monsters still remaining in the area. Jason is put into a near-death state, with Hera and Thalia both believing he is dead. Thalia blames Hera for this and tells her to revive Jason but she stated she can't. Piper says he is breathing, something that Hera doesn't believe to be possible. Piper then uses her charmspeak to awaken Jason, much to the relief and surprise of everyone.

Holographic Scroll - Leo's own invention, used in The Son of Neptune to alert Camp Jupiter that the Argo II is coming. A few days after his death and resurrection, Leo used another one to send a message to his friends at Camp Half-Blood. The house turns out to belong to King Midas and his son Lityerses. At first, all seems to be going well until Midas turns Piper into gold and when he tries to fight him with his fire, he can't (the gold suppresses his powers). He is also turned into a gold statue but is freed after Jason defeats Lityerses and washes off Leo and Piper in the river, which is freezing cold. Jason uses the storm spirits to fly them away from the house and after setting up camp, Leo makes tofu burgers for Piper and the newly freed Coach Hedge. As a member of the Seven and a son of Hephaestus, Leo is extremely powerful and had displayed excellent battle skills even without formal training. Jason remembered Octavian from Camp Jupiter and hated him, knowing how persuasive he was. Jason learned many stories and legends from Camp Jupiter, including the Mark of Athena and the story of Cupid and Psyche.Several days after Gaea's defeat, Jason visits Nico di Angelo with the intention of convincing him to stay. The son of Hades, however, had already chosen to anyway, making a very excited Jason hug him.

In The House of Hades, Leo felt guilty about Percy and Annabeth and knew it was his fault, but knew that moping around wouldn't save him. However, after meeting Calypso, Leo felt a surge of anger towards Percy, and was mad at him for hurting Calypso. To make things worse, since Calypso clearly still had feelings for Percy, which made things ten times worse for Leo. Ultimately, however, Leo is the one to save Percy and Annabeth by flinging a screwdriver at the Doors of Death, managing to save them just in time. Leo was very happy when Percy survived Tartarus and whooped in happiness. When Thalia found Beryl, she was sobbing at Stone steps of the Wolf House and said that Jason was claimed by Hera and left for dead, and was inconsolable for days. Thalia ran looking for him, but she couldn't find him. Thalia called the police, who questioned Beryl for a long time. Thalia and Beryl subsequently fought for a long time until Thalia ran away, now that Jason was gone. Thalia never learned the truth about her brother and thought he was dead until The Lost Hero, and never told anyone about him, not even Luke and Annabeth. This is similar to Nico, as in The Tower of Nero, Will states that Nico slips into Italian when he's really upset. After that, Percy and Leo were friends with no problems and they defeated Nike with the help of Frank and Hazel. Leo became sarcastic and joking with Percy, calling him "Water Boy", which he told him not to call him, then calling him "Aquaman", which he hated more. Leo was also miffed and asked him why he had to destroy the plumbing when he did. Percy also joked that if a statue engulfed people in fire, he should send Leo, and Leo jokingly said he loved him too. Leo was also grateful when Percy got everyone in the crew, including him, gelato, and said that it made his whole day better. Leo also joked about how Percy's zodiac sign was Leo's name. However, Leo kept his suicidal plan to sacrifice himself from Percy. Percy was devastated when Leo died, and was initially angry at Hazel and Frank, but his anger subsided when they cried and agreed that it was a plan Leo would've done. Percy was hopeful that Leo was alive and said that if he lives, they can take turns strangling him.

Upon returning to Camp Jupiter and the defeat of Polybotes, Leo appears on a video scroll that was sent to Percy through Ella. He told them that he would appreciate it if the Roman demigods didn't shoot them out of the sky when they come to rescue Percy and start their quest. While watching the video, Hazel mistook him for Sammy Valdez and Percy remembers the picture of Sammy when looking at Leo.

Hazel Levesque and Leo first meet in The Mark of Athena, but first sees him in a video scroll during The Son of Neptune. When they meet at Camp Jupiter, Hazel is very suspicious of Leo and kept frowning and looking at him. They first had a proper conversation in Salt Lake City, and he found himself to be infatuated with Hazel. Hazel studied Leo, which made Leo feel self conscious, but also wondered if they met before. Hazel and Leo ended up going on Arion to Salt Lake City together after Hazel insisted. Leo liked Hazel even more after he found out about her story from Percy, and thought she seemed warm and alive, and good with people. He knew he should keep his distance from her since she was dating Frank, but thought her hair smelled good and riding with her with his hand around her waist made his heart race. Eventually, Hazel brought up the subject of Sammy with Leo, saying he looked so much like him, which embarrassed them both. While travelling through the city, they had plenty of awkward moments, like when Hazel caught Leo's hand when he almost fell, making the two be face to face. But the two became friends after they defeated Narcissus. Once the Argo II made it to Delos, Leo wanted Hazel and Frank to come with him because he trusted the two more than the others to know about his suicidal plan to sacrifice himself. Hazel was very upset when she heard the news, and a tear fell down her cheek. Leo told Hazel that she was the only one who could cover for him, since Sammy knew how special she was. He said that he blessed him when he was a baby because he knew that Hazel would help him, and that everything was leading up to it. Hazel burst into tears and hugged Leo. Hazel said that she hated the plan, but she would do it for him. Hazel ended up making. Fake mist version of the Physician's Cure and gave it to Piper.Jason has had daily audiences with Auster, the Roman god of the south wind, in connection with the Seven being able to proceed on their way to Epirus. Jason got very tan during his stint in Africa but very annoyed at Auster. After five days, Nico spoke to him and asked if there was any word from the king. Nico told Jason that they needed to leave soon and he sensed a bad feeling about the doors. He then said he had to convince Auster to help them, since he suffered too many humiliations. Jason then tried to discuss what happened in Croatia, saying he understood him and no one would judge him, but Nico grew angry, saying he doesn't belong anywhere and he would never understand since he was everyones golden boy, but no one ever accepted him except for Bianca, with no say in how he felt. Finally, Jason told Nico to take a chance and trust him, and that its better than hiding, and even called him out for always running away and hiding, but Nico snapped and said he would help him then leave forever. Jason began to think being friends with Nico was more trouble than its worth. Jupiter | Juno | Neptune | Pluto | Mars | Minerva | Ceres | Lupa | Bellona | Fortuna | Janus | Terminus | Vulcan | Mercury | Apollo (Roman) | Diana | Venus | Bacchus | Pomona | Aquilon | Hercules | Cupid | Auster | Favonius | Letus | Victoria In The Blood of Olympus, Leo recalled how he used to play with plastic organ models as a kid. He once got in trouble after turning a cross-section kidney and some skeleton legs into a kidney monster, and scared the school nurse. In kindergarten, he was taught how to sign his name. The four planned to defeat Nike with Hazel raising the labyrinth and Leo have everyone gadgets to use to defeat her. Percy and Leo fired fake grenades that were popcorn, and distracted the Nikai. Eventually, he and Percy hid, and Percy apologized for failing Calypso, in case he didn't make it, and reassured Leo he would do anything to help them. Leo was grateful and accepted his apology, no longer able to resent Percy. Suddenly, Hazel got injured and Leo wanted to help her, but Percy told Leo to defeat the last Nikette while he helped Hazel. He defeated the last one by throwing fire at her, making her melt. Nike was furious, but Leo used the archimedes sphere to tie up the goddesses and force them to go whole with celestial bronze netting. Leo went to go find Percy and Hazel and complimented Hazel, saying she was amazing. The four then went to Nike and they learned that one of the seven would die, but they needed the Physician's Cure. They then put her in a horse stall on the ship. Leo began spending time with Nike to get advice for his plan to sacrifice himself.

The four arrived at Olympia and he searched the museum with Percy. They sat on a bridge overlooking the Kledos river, and it was very awkward for Leo to hang out with Percy due to their history with Calypso, and him being a survivor of Tartarus. Percy noticed that Leo was looking at him angrily and asked him why, and said that they should talk. They were interrupted by Hazel and Frank, who could not find Nike. The four looked around the ruins, which Leo was not impressed by, annoying Hazel. The more into the ruins Leo went, he became more uneasy, thinking about his past. They stopped at the Temple of Zeus, and Leo realized that was where Nike most likely was. Leo and Percy managed to summon Nike by saying that Adidas was better, and Nike and appeared. Leo asked Nike what was going on, and she split into her Roman form, Victoria. Both goddesses said that they had to fight Greeks versus Romans: Leo and Percy versus Frank and Hazel, and has to fight the Nikai. Leo tried to talk her out of it, but it was no use. The Nikai chased them and they had tone hide.

Despite his easygoing attitude, Leo is emotionally scarred from the death of his mother as he blamed himself for most of his life for causing her death. He hid a hurt and angry demeanor with humor until realizing that his mother's death was not his fault. Leo's serious side exhibits when he is angered by someone, when those he loves are threatened, or when the situation calls for it. He is also frequently seen building small machines and gadgets, and is very skilled and serious about his work, having built a large portion of the Argo II on his own. He is able to funnel his nervous energy into mechanical solutions to seemingly insurmountable problems. Leo has a tendency to view even the most emotionally-charged situations objectively, which Calypso disapproves of. This causes conflict between the two. He also feels that his whole life has been nonstop danger and running, which is reflected in his abundance of nervous energy and need to always fidget and keep his hands moving. Since the House of Hades, Jason had nightmares about Gaea. Sometimes in Epirius with Clytius, some with Gaea destroying Camp Half Blood, and one with Lupa killing him after revealing her true form and his mom leaving him. In the last nightmare, he would be scared and wake up with tears. He was also very worried about Reyna, Nico, and Hedge. Especially Nico, and he would pray to his father to help him after everything he'd been through.