Ship Leesoo (십이수, Shib Yisoo; "Shibisu") is a C-rank Regular. He is relatively weak, yet possesses a great ability to deduce and an intellect on par with Khun's. Nonetheless, he made it past all of the tests on the Second Floor, where he was assigned the Scout position and is now climbing the Tower as the leader of his team. He is currently on the 52nd Floor.
Leesoo says that he wants to climb to the top because of a promise to his friend.
Leesoo is surprisingly intuitive when it comes to people's motives and feelings. An example of this is when he knows Khun is bluffing.
Khun Aguero Agnis and Leesoo are both characters that use their heads, but while Khun's specialised towards tricking and improvisation as well as being smart, Leesoo is totally the academic genius.
His name means that he is a serious repeater. Shibi means twelve in Korean, and Su is often used to describe how many times a person has repeated the test. For example, if you fail a test and retake it, you will be doing Je-su, if you take it for the third time, it will be Sam-su, and so on.
SIU once said that Leesoo is one of his favorite characters because he likes characters with wits 
(While facing Ho and Serena Rinnen) "Thought infuriating, it's true. Since I'm not very strong. But - I've at least got the guts to stand my ground even in the face of death. So you better be careful."
(To Anak Zahard) "I don’t know what you’re hiding from me! But I know enough to say this! You are in the same place as me right now! And you are in the same team! I am your friend standing by you right now! I don’t know what kind of a past you had or how great of a future you might have, but the person who’ll stand by you right now is ME!"
(Thinking to himself) "The reason I managed to get this far is not because I'm outstanding. And not because I'm strong or smart. I just had outstanding people around me. And because I trusted them."
(To Khun Aguero Agnis) "In the end, the reason why those who stole from me did it was just because someone else stole from them as well..."
(To Ja Wangnan) "We have goals of our own so we can't stop. Hurry and catch up to us. Next time we meet, be stronger so we can have a match."
(Talking about Devy to Hatsu) "People who used to be poor or weak will always carry a kind of trauma with them. Sometimes they develop a mean streak and end up turning on people who are weaker than them. But once in a while, there are people who help out those in need because of what they went through in the past."