2. Lee Ik Jun

     One of Ik Jun's defining characteristic is his cheerful personality, which for his best friends, "cheerful" is just another way of saying he’s crazy. He appears to be the most easy-going person among the squad. He treats everyone as if they're close friends, willing to listen to their stories even if it takes his time. He is also good at keeping secrets, although according to Jun Wan he likes to tease people with that secrets you share with him. He likes to wander everywhere, talking to everyone & helping them if he can. He, for instance, helps cover a job of a friend in the hospital's cafeteria, he takes care of a dead patient's son so his mother can take her time grieving for his husband, he helps Jang Gyeo-Ul’s relationship with Jeong Won, et cetera. Although he seems to be a sociable person, according to Jeong Won, he doesn't seem to be the person who's easy to figure out.

    Ik Jun is good at everything he does, it makes him lack inferiority complex. You name it: he's a skillful HPB doctor, back when he was a student, he always gets the best grade even when it doesn't seem like he spent his time studying, moreover, he can actually sing & play guitar, he also has good social skills & is a good listener. But having these qualities doesn't turn him into a self-absorbed person. Instead, he tends to put others' feelings before his, such as that time he canceled his plan to see Seong Hwa to be there for Seok Hyeong who was just turned down by her. When his ex wife divorces him, he doesn’t hold grudges even when he may have reasons to. His positive outlook towards life helps him handle things in a calm attitude. At times, this quality also impacts his patients positively, encouraging them to hold on to hopes and keep on living.

    Ik Jun used to live the life of a party, but not anymore since he has U-Ju as his son & becomes a single parent. Now, his son has become the center of his life.

3. Ahn Jeong Won

    Jeong Won, also called Andrea, is a Pediatric Surgeon who deeply adores & loves children. He's not aware of it, but his patients' condition has a lot of impacts on his mood & behavior. For someone like Jeong Won, real happiness is felt when he sees others feeling happy. Indeed, he has a delicate heart, making him sensitive toward others' feelings. He's the kind of person who would notice the slightest difference in your behavior then ask if you have a problem.

    As a member of a conglomerate family, his friends find it weird that he often runs out of money & isn't interested in wealth or taking a higher job position. Rather, he uses his wealth privilege for the patients who need funding help. Having a kind & warm personality makes people call him "Buddha", even when he's a Catholic and dreamed of becoming a pastor. But, of course we can't expect someone to always be a saint. He's told to be warm to everybody but his close friends. He holds grudges & remembers little things his friends did in the past that upset him. He's also really thorough, likes things to be super clean. It makes Song Hwa suggest that he sees a psychiatrist. He's also a doctor who smokes cigarette (taught by his mom).

    Among his friends, he’s the last person who would appear dating someone. He's strong-willed about what he wants that nothing appeals to him other than his dream of becoming a pastor. He’s been focusing on that dream until Jang Gyeo-Ul, someone who clashes Jeong Won's warm personality with her cold personality, enters his life, redirecting his thoughts. Their encounters make us see the other side of Jeong Won. Although he has warm traits, he acts cold towards a woman who shows interest to him; whereas with a cold personality like hers, Gyeo-Ul never hesitates to express her feelings.

4. Kim Jun Wan

    Jun Wan is a competent cardiothoracic surgeon. He begins the drama as a severe man who scolds his juniors every time they fail to treat their patients carefully. He's annoyed when others are being nosy. But underneath his not-so-friendly attitudes towards his juniors or even patients, Jun Wan is a generous, caring, & somewhat anxious guy. He buys meal for the medical students; he rarely say kind words to his junior, but he always gives appreciation if his junior does well, as well as willing to do anything he can to help him (e.g. being the chief of department to help Jae Hak); he won’t give up rescuing his patients' lives even if the chances are small. To conclude, he does have affections towards others, but rarely convey his feelings explicitly.

    Jun Wan always handles things in a composed manner, but there are times when he can't help but feel anxious about something, mostly about Ik Sun. For Jun Wan, Ik sun is the embodiment of someone he longs for. All this time, it's a rare case that he lasts long with a girlfriend. Therefore, he's willing to hold on to her that it makes him anxious at the thought of losing her. Even so, he remains to act calm & hides what he currently feels.

5. Yang Seok Hyeong

    Unlike Ik Jun, social interaction isn't Seok Hyeong's forte. He likes to be alone, prefers text messages over phone calls & tries to avoid social situations when he can. This makes some people have a hard time interpreting his intention, assuming he doesn't care about other people. On the contrary, he's a deeply understanding & caring person, it's just that he tends to show his caring gesture through his actions more than his voice. The complexity of his personality makes him appear as interesting for some, including Chu Min-A.

    As a gynecologist doctor, he always treats his patients with a warm attitude that they are willing to get in line to have a consultation with him. And although he finds pleasure in being alone, he cherishes his moment together with his best friends. In fact, he’s the one who initiates the idea to his besties to spend every weekend together by playing music. For him, his friends are a source of comfort & a place where he can share anything with. There aren't many people out there who can serve that  roles, let alone his broken family.

    Just like Jeong Won, he's a son of a conglomerate father but refuses to live from his wealth or take over his position. He hates his father for ruining his family, yet he never let anger overtake him. He'd rather avoid conflicts than confront it. If anything, he tends to believe everything is his fault, just like how he feels sorry for his ex wife. This family problem has led him to grow really fond of his mom & spoil her with affection much more than before.