Though I usually don't care much for fashion related manga, The One has an interesting set of characters and circumstances.
Eros, or Yin, is a fashion director with an extremely famous model of a twin brother, Angus. We learn through the chapters that Eros in fact was raised by his mother. His father (a royal) never saw Eros as his son, so Angus was raised with his father instead (noted because Angus and the father had the same eye color). Eros's mother eventually became ill and insane and committed suicide. When she became ill, though, he was sent to live in a youth center. He has a fair ability to fight, so being bullied was never really a problem for him within the center. This ability, though also got him in trouble with much worse things outside. He was eventually taken away by a group of druggies. From there, his past becomes cloudy. It was probably during this time that he received a gunshot wound, making the scar that he now has. It would then make sense that he was discovered by someone and met up with his step-father, or rather, foster family. From there he became a fashion director.
All that being in his past, it makes perfect sense why his attitude is usually so cold and perhaps cynical at times. He met the model LeLe (main character) when he was disguised as a bum one day (a strange hobby of his). He then met LeLe again at her debut fashion show in honor of her dead mother, and she quite literally fell off stage and into he and his brother's lap. Once again, he managed to find her when he was disguised as a bum. Her perseverance and shining outlook on life, despite having only her grandmother as a guardian took his icy heart for a ride. It can probably be said that for the first time she made him care.
After that, they met again once when she was doing a photo shoot away from home for the first time. After a rather nasty run-in at dinner one night, the two started to become solid friends. He often teased, but his advice was completely solid, and by the time she flew back home, she trusted him. She even went as far as to give him an earring.
The fact that he had not previously pierced his ears, and yet ended up doing so after he received the earring made a statement of exactly what place she had in his heart. This was probably even more apparent when she flew to New York and ended up getting very drunk at a party. Eros, having been invited, due to being friends with the person holding LeLe's contract. Even so drunk she's almost completely passed out, Eros managed to wake her. Upon seeing the earring, she runs over to him and clings to him. Its then revealed that he knows her full name. He safely gets her to her new apartment. Then, the next night, when she drops off the radar, threatens to do horrible things to his manager friend if he doesn't find her.
From there, its a string of games played, advice given, and chance encounters. He kisses her several times in this span of time. Once purely out of feeling, once perhaps because LeLe blackmails him a little, and another time just before he burns all they have between them to the ground. On the last occasion, Eros's brother has been threatened, and so he changes his looks. LeLe confesses her feelings to him, and he appears to brush her off. She then confronts him at a reception fro LeLe and Angus's latest works. Eros then, after being confronted, attempts to rape her. Leo (her gay roommate, and Eros's personal friend and employee/co-worker) manages to stop him before things get serious.
But here's where things get weird. He coldly runs leaves the scene and her behind in Leo's care. We know that LeLe falls ill later. But Eros later that night has a fist fight while a building, injuring his hand while he remembers how he hurt her. There's also a scene where he's hiding behind a wall and he listens to a man report that LeLe is nothing more than "the twin's play thing," but is asked to keep watching her.
Leo later confronts him at work, and Eros shrugs it off until Leo slaps him across the face in front of his entire staff. LeLe, after some tender care recovers and is offered a job in Paris(?). Its then that LeLe, by chance again, come face to face for the first time since the incident. He coldly addresses her, and she retaliates. She makes the statement that she in fact not only doesn't want to be his lover, but she also no longer wants to be his friend. She even questions whether they were ever friends. He, having offered her more care than he had ever shown anyone before, was frozen to the spot after she walked away. At this point, we've known for quite some time that their father intends to bring Angus back to his country by force. Eros arranges for Angus to be sent to his step-father's home, while he is dragged off to the father's home. From there, the story hasn't progressed at all, so we can only guess what happens next.
Eros as a character has a lot of past baggage and many habits that he cannot break (smoking when he works, acting like a bum on his days off). He appears cold on the outside because of all the pain he has endured, but for all his callouses, he is quite wise. He understands how things in the world work and have seen them from every angle. His feelings for LeLe are probably very complex... ones that make him care like a father and want her like a lover. This might even be the reason why he hasn't revealed his own feelings to her. His methods are often harsh, but he seems to go for the greater good in the situation.