Yoosung is a really nice and lovable person, and is described by the other RFA members as 'a real puppy'. Yoosung cares about people a lot and loves to spend time with others. He is naive and believes things that are told to him more often than not, as shown during several of his interactions with 707. As a result, he is often unforgiving to his naive nature.

Despite his somewhat naive and lighthearted nature, Yoosung is severely depressed after the death of his cousin, Rika, with whom he had a very close relationship with and who he idolized. After the death of Rika, Yoosung lost all interest in his studies and becomes a shut in, rarely leaving for classes and opting instead to play LOLOL in order to cope with the crippling sadness.