Ship turned up on the Second Floor with all the other Regulars. He explored the field around him and then accidentally ran into Anak and Hatsu, who were fighting. He freaked out because of them but managed to avoid being killed and was going to run away when it was announced that the Regulars had to form teams. He was shocked that he would have to team up with two very powerful Regulars and got scared about it but realized he had no choice and approached them. They completely ignored him, which actually made him annoyed. He grabbed onto their shoulders as the timer went off, qualifying them as a "team".
He then tried to convince Anak and Hatsu that he was actually not useless, by saying he was trained in the "killer arts". He barely managed to get through Lero-Ro's shinsu barrier, with his face bloodied, However, he aced Yu Han Sung's door test, deducing the answer better than even Khun, in only about a minute. He was the only Regular to figure out the whole answer all on his own.
His team went into the Crown Game, to try and ascend to the next level early. Anak sat on the throne while he and Hatsu fought the attackers. Leesoo came up against Ho and Serena, and was able to hold them off for a little while despite being unarmed. However, when they attacked him in conjunction, they gained the upper hand, but Hatsu turned up and defeated both of them easily. He and Hatsu were then blasted away by Phonsekal Laure. Anak stopped attacking and jumped off the throne to make her bet with Baam, resulting in the team's disqualification. Leesoo watched the rest of the Crown Game from his team's cell.
He was then assigned the Scout position and seeded first. He managed to get on Khun's "friend" list during training. In the Hide-and-Seek Test he was put on Team A and used as bait to attract Quant. He managed to get Quant to drop his guard, but the Ranker proved to be tougher than expected and the plan failed. Leesoo then teamed up with a few other Regulars to try and delay Quant and showed courage in trying to fight him, but they were all easily blown away.
After the test, as Khun lamented their failure, Leesoo told him that they had done their best, and that Team B would probably fail as well. He then noticed that Laure had been holding a rude sign over his shoulder and tried to kick him.
Leesoo did not reveal Khun's scheme to the others when Khun manipulated the others into helping Baam in the Submerged Fish Test because he sympathized with Baam. Later on in the test, he stood defensively over Anak when she was attacked by Lo Po Bia Ren after he led Ha Yuri Zahard to the scene. Leesoo was entrusted with the Wing Tree insignia by Yuri to give to Baam. After the test, he showed distress over Baam's death. He felt like he owed a debt to Baam and backed up Hatsu's and Khun's plan in helping Baam's wish: To get Rachel to reach the top, recruiting the others for the cause.
In a spoiler posted by SIU, Khun spoke to him about his sadness over Baam's death. Khun suspects foul play during the test and wants revenge, stating how Leesoo and the others were tools for this. Unlike the others in the Part 1 team, only he and Khun are aware of the fact that Rachel has tricked them. This secret is kept only between him and Khun, as Khun stated that "I don't want to ruin the team that Baam so wished to protect".
When Khun split the team into two, he put Leesoo in the trailblazing team designed to attract attention. It is possible that Leesoo is the leader of that team as he is smart and it is unlikely that the two Princesses who are in that team, Anak and Androssi, would listen to each other's orders.
Khun contacted Leesoo, telling him that Rachel, without a doubt, tricked them.
Khun had just passed onto another Floor and broke the good news to Leesoo. Leesoo said that they tried the 30th Floor test but failed. He also mentioned that they could only try once a year. As Androssi and Anak were arguing over a football game, Khun and Leesoo resolved to meet each other in the factory round.
When the news that Khun had "died" reached Leesoo's team, he watched grimly. When he got the invitation to the factory round, he led the team out the door, telling them that they would find Jyu Viole Grace and crush him.Archimedes, Hatsu slashed at the window in front of him, bemoaning Leesoo's descent into idiocy. That evening, he and his team had a live press conference in which he stated that he wasn't worried about Jyu Viole Grace; however, Khun could see through his bluff.
He, Hatsu, and Anak were running from their lodgings to the centre of battle when Androssi appeared, carrying four Regulars with her. They told Leesoo where the FUG had set up base and the three of them left to attack. They put Anak up on the observatory, but this was just to gain time for their other teammates to get into position. Once this was done, Leesoo went with Vespa through the sewers to the first floor. There, they met Yuto and he and Vespa worked together to almost defeat Yuto. However, this plan was foiled by Viole, who appeared in the nick of time. Leesoo sealed Viole's shinsu by having Verdi steal it and sent Amigochaz and Vespa to capture him. Yuto protected Viole and got poisoned, resulting in Viole using the "Thorn" in order to defeat Amigochaz. He was astounded when both Amigochaz and Vespa were defeated by physical strength alone, wondering how his previous information could have been so inaccurate. He was reluctant to surrender and only did so when Verdi informed him that there was someone at her location. Frustrated, he admitted to himself that he had underestimated Viole due to his thirst for revenge and gave the order to retreat. After giving Viole bullets and honey, he, Amigochaz, Vespa, and Laure left for the rendezvous point where the whole team shot each other.
Leesoo was drinking on the poolside when Anak came up to him with Ron Mei, a teammate of the top E-rank Regular, Yama's Mad Dog. They exchanged pleasantries for a bit, but despite the confident act, Leesoo was worried for Amigochaz who had yet to heal and Hatsu whose sword broke. At night he gave Hatsu a cell phone with Emile to seek a new sword with it.
He asked Anak for the disappearance of Hatsu and at the start of individual battles, he was chosen as one of 10 Gamblers of the event. During the first round, he bet Miseng but she lost against Prince, Akraptor and Wangnan. Before they started the last round, in which you could get a 3 million point bonus, he was tied with Rodni and, in the battle between Anak and Ran, he bet everything on his teammate. During the last battle, he was worried because Anak carelessly fell into Ran's trap. He was disqualified from the bets after the intervention of Parakewl.
During the meeting of gamblers, he was arguing with Ron Mei and acknowledged that Mr. Mask was a fairly intelligent person.
Leesoo was bothered by Anak's words about Viole and Androssi's strange behaviour as they began the Development Tournament.
During the Development Tournament both Vespa and Leesoo were brought up to speed by an injured Hatsu on the creation of the worst weapon and the revelation that Baam was alive. He later met up with a confused Khun who he greeted with the annoyance of being kept out of the loop.
He briefly lent his aid against Beta, from his carrier and later forfeited the game to allow Viole to be summoned.
After Reflejo challenged Viole, Leesoo and Vespa went off in search for Novick, one of the hostages. At first, their search was fruitless, but after Xia Xia revealed their locations, their luck began to change. After successfully finding Novick they were all flown out of the cavern on Vespa's 'adult' form where they met up with Androssi, Hatsu, Khun, Baam, and Rak. After evading a hairy situation the Regulars escaped aboard the Wolhaiksong escape ship.
He was seen getting drunk while the Regulars were celebrating their success in the Workshop Battle.
He was with Prince and Akraptor when Wangnan woke up. He greeted the Regular and told him to take care of Baam as the leader of Team Tangsooyook.
He said his goodbyes when his team was leaving to begin climbing the Tower again.
He called Khun and casually conversed with him about the recent events while being bossed about by Androssi. As Leesoo was seen with the rest of his team, he told Khun to come up where they'd be waiting for them and then he finally congratulated Khun on becoming "The Three" again.
While watching Team Novick fight other regulars upon arriving at the station, he and Androssi agreed that Khun Ran would regret using so much power so early, then told the rest of his team that they should prepare to hunt the "Kaiser". Upon seeing Ran fight Hesse, one of the ten bosses, the two re-evaluated their previous stance, noting he just got more powerful.
After Team Novick was drugged by Chigrinsky, Leesoo's team arrived, having Hatsu slice Chigrinsky in half before he could steal any names. After his team and Khun Ran cleaned up the room, he learns Novick's team beat the Hell Train regulars to the Name Hunt Station. Leesoo explains that climbing with Anak is becoming more dangerous for the team and that Androssi has been coming under fire politically from the other princesses, especially Lo Po Bia Lilial and Shilial Zahard. They made a deal with Androssi and the team that if she could hunt Kaiser's name, the Lo Po Bia family would not interfere in her affairs and that they would hand over Lo Po Bia Ren. However, Androssi lost her first duel with Kaiser, so Leesoo and his team began to hunt the bosses in secret in hopes of going to the festival for a rematch.
To bring the remaining bosses out of hiding, Leesoo devised a plan to use Baam acting as Jue Viole Grace to lead a revolution and liberate the no-named. While he convinces Novick's team to play along, Aguero catches on, telling Leesoo through his pocket he will kill him when he sees him.
Later, he waits for bosses to appear, wondering with Hatsu whether Kaiser was more cautious than he thought. Hatsu tells him it's the opposite: Kaiser himself will challenge Viole. Moments after Hatsu's prediction comes true, Leesoo contacts Androssi and gets her to pull Baam out of the confrontation, retreating to his hideout.
At their hideout, Khun hears Leesoo's plan but refuses to let Baam help their team since he needs Kaiser's name himself to honor Yuri's challenge. Leesoo is shaken by this revelation and is powerless to stop Hatsu and Aguero from fighting each other, letting Aguero leave in the end. Afterward, he laments the necessity of using Viole, saying only his influence can save Androssi.
When the festival begins, Leesoo is shocked to see the announcement that Viole will fight Androssi during the auction, and makes a deal with Aguero to help free the hostages and hunt the rest of the bosses. He takes a hidden path with Hatsu and Androssi, leaving Anaak and Vespa near their hideout to deal with bosses hiding nearby.
At the escalator to Kaiser's chamber, he intercepts Aguero, Baam, and Red Greymon, lamenting the competition of their teams and haphazardly tossing the Shinsu Bomb towards the escalator, blowing it up. However, Leesoo's true intentions were to help Baam's team get to Kaiser without being blown up by the bomb secretly installed into the escalator, allowing them to safely proceed.
Leesoo then finds Hatsu and Shilial, informing them that Jue Viole Grace is already fighting Kaiser and their current fight is pointless, telling Shilial to retreat with her sister unless they want other princesses to believe they inadvertently helped Viole win. He then wonders whether the sisters wanted to prove themselves to Arie Rose Zahard or Hendo Lok Gladmerry Zahard, but Shilial responds by telling him they sided with Khun Maschenny Zahard instead, leaving with her sister to report back to a princess "Maria."
After the battle with Kaiser, Leesoo meets with Aguero, informing him of the Princess' plot with Maschenny and Maria. He then watches the auction, commenting on Kaiser's attractiveness. Later, back at his team's hideout, the two discuss the fate of the station and their teams' respective journeys ahead. At the bridge to the Hell Train during Yuri and Evan's battle with Karaka, Leesoo and his team say their farewells to Baam's team, telling them to be careful and to take care of Androssi, who decides to go to the Floor of Death with them.
Leesoo arrives at the last station on the 44th floor in a ship with Hatsu and Laure, excited to welcome Baam and his team as they exit the train. He is surprised when Hatsu tells him about the fleet of ships also gathering outside.
He and his team sneak into the Warship Rest Area to investigate the reason the fleet has arrived, sending Vespa and Verdi to conduct reconnaissance. He grows annoyed at Verdi's eccentric reporting, and wonders if he should wait for his acquaintance Benny's crew to arrive to gather more information. He tries to stop Hatsu from breaking into their meeting and threatening them to reveal their plans but fails, then listens anxiously as they reveal their true reason for arriving: To capture and kill everyone aboard the Hell Train.
Leesoo arrives in the middle of the battle in a large warship with the rest of his team in an effort to save Baam as he runs away from Kallavan.
He begins to explain how they arrived, but the situation is too urgent and he opens the dock so that Baam and Androssi can enter and escape. He runs to greet Baam, hugging him as the latter breaks down and sobs. Later, he goes to see Aguero, learning of his current state through Hockney. When Rak tells him there's a way to wake him up again, he offers to help since they're all on the same team, much to Vespa's annoyance.