|First Appearance||Vol.1 Chapter 7|
Twenty-Fifth Baam: Leesoo and Baam are relatively good friends during Part I. Like the other characters, he feels indebted to Baam after he changed the rules so that the entire team could pass.
Koon Aguero Agnis: Leesoo and Koon are on good terms with each other. As the two smartest people among the Regulars, they collaborated closely during the tests. Though Koon always has hidden plans on the agenda, Leesoo is sometimes capable of seeing through them.
Anak Zahard: Apart from Androssi, Leesoo seems to have the deepest relationship with Anak. Even though Anak hid the fact that she was the daughter of another Princess, he still trusted her. For some reason during Part I, Leesoo kept calling Anak his daughter.
Hatsu: Hatsu and Ship teamed up during the first test on the 2nd Floor. Though they were shaky at first, the two became friends rather quickly. Hatsu at first found Leesoo annoying. Then he saved Leesoo during the Crown game. Later, Leesoo helped Hatsu pass the Positions tests. Leesoo's friendly personality cooled down Hatsu's flaming one, in order to collect teammates for the Scout position's friendship list homework assignment.
Black March: Anak thought that Leesoo was a handsome man, so she asked him to speak to the Black March, the March however disagreed giving violent electric shocks to him.
Koon Aguero Agnis: Leesoo and Koon are still on good terms with each other. Leesoo is the only person who Koon trusts to lead the other team and to share the secret of Rachel's betrayal with. Leesoo is seen sitting with Hatsu, Anak and other Regulars from Part I, looking grim at the news of Koon's death. He targets FUG in order to get revenge, disregarding the risks of failing the test.
Jyu Viole Grace: Leesoo holds great hatred for Viole because of Koon's "death", not knowing that Koon is alive and that Viole is Baam. He attempts to get revenge by capturing him and killing the other FUG members at the risk of failing the test. Viole attempts to resolve things peacefully because of their friendship, but hides his true identity. He later expressed enormous surprise that Viole was Baam.