Seongmin's Links
Seongmin sees Ji-Yu as a younger and prettier version of herself causing her to feel that her position at the company is threatened by Ji-Yu. She is not overtly rude to Ji-Yu but can tend to act very condescendingly and passive-aggressively towards Ji-Yu.
Ji-Yu looks up the Seongmin because Seongmin has been in the industry longer than Ji-Yu. She is aware that Seongmin does not seem to like her, but she is unaware of the degree of Seongmin's dislike toward her. Despite this, Ji-Yu tries to remain as polite and professional as possible with Seongmin.
Seongmin is somewhat aware of Seojun's feelings for her in that she does know he has feelings but is unaware of the intensity. Seongmin finds Seojun attractive and sweet, however, she is not looking for a long term relationship. She enjoys being the center of attention so naturally, she treasures his feeling for her; not only in a selfish manner but also as they are good friends. She does humor the idea of a relationship together since she likes to "have options".
After co-starring in a drama where both play the other's love interest, Seojun is truly in love with Seongmin and believes that she reciprocates his love. He is very flirty around Seongmin (though she lets him be) and dotes on her. Seojun is very chivalrous and always praising Seongmin for the smallest things.
To put it bluntly, Seongmin couldn't care less about Jae. Internally, she envies the deep love and connection Ji-Yu and Jae seem to share. She is often curt and dismissive of Jae on the rare occasions they do interact.
Jae is, admittedly, not Seongmin's biggest fan due to the way that he sees Seongmin treats his girlfriend, Ji-Yu. He is quick to defend his girlfriend when he sees that she is put in a tough spot by Seongmin. He remains civil and polite only because Ji-Yu wants him to.
Having briefly dated Min-jun when she was 21 and he was 22, their relationship lasted 6 months before they mutually broke it off. Seongmin still cares for Min-jun and is attracted to him but does not wish to be in a relationship with him for now. Occasionally, Seongmin will be flirty with Min-jun purely in a playful manner.
Like Seongmin, Min-jun cares for Seongmin but is not interested in a relationship with her. Though he does find her attractive and good company, her possessiveness of him while they were in a relationship was a big red flag for him. Min-jun debuted only a month before they broke up. They both agreed that they were not compatible as romantic partners and decided to focus on their careers.