He is an older brother figure to the female lead with no blood relation. They know each other better than anyone else, and to her, Sylus is someone who is full of mischief but whom she always relies on and trusts. After becoming the commander of the Deepspace Fleet, he presents a facade that seems devoid of emotion. While he acts as a cold wall to the people in the fleet, the way he approaches the female lead and smiles warmly at her as he always did is reminiscent of a double personality. Having cherished and looked after the immature female lead since childhood, he shows an extreme obsession with this relationship as a brother who dotes on his younger sister. Among the male leads, he has the strongest possessiveness and obsession toward her. He believes in unconditional protection and keeping her by his side, stemming from a compulsion to protect her since they were young. He even spits out lines heavy with obsession that reveal his thoughts or values, and then distances himself slightly if things become awkward. Having returned alive after being presumed dead, he now has many secrets he cannot tell her. There are frequent stories of conflict between Sylus, who tries to bury these secrets to protect her, and the female lead, who wants to find out and be with him no matter what. They stayed together even when they were in the research center after the Deepspace disaster occurred. Adopted by Zhang Shu, she called him 'Oppa' throughout their childhood and they were siblings on paper. However, with the deaths of Zhang Shu and Sylus, the family structure disappeared and the adoption relationship was terminated. Nevertheless, he tries not to make it obvious to her, suppressing his feelings while trying to develop the relationship slowly. Perhaps because of this, he expresses his feelings for her ambiguously. He isn't very good at hiding the fact that he likes her. He is involved in unfavorable connections with the Fleet and Ever. He has never had a girlfriend or other women around him besides her; moreover, in high school and college, he often asked her to play the role of his girlfriend. Therefore, Sylus has never had contact with any woman other than her and is a virgin.