I have put this together from different sources, mainly the TVN website. I thought it might come in useful :)

Characters:

Main

Ryu Sun-Jae

He was a top star with everything, from good looks to talent and charm. A former swimmer turned singer and actor, his life as a celebrity didn't end well, ultimately leading to his unfortunate death.

Sun-Jae was the ace of his school's swimming team. He won two gold medals in the national sports competition, set a record comparable to Park Tae-Hwan in the main event, and will be in the media spotlight as a next-generation sports star.

Because of his shoulder surgery and rehab, his once-promising career has come to a halt. He focused solely on swimming and family until something new entered the picture, capturing his mind and heart.

On a day of rain showers, a girl named Im Sol, who lived opposite his house, put a yellow umbrella over him, and his heart skipped a beat. He fell in love at first sight but never spoke to her.

Because of irreversible damage to his shoulder, he couldn't fulfil his dream of being an Olympic swimmer. So he followed his friend In-hyuk to an audition and made his debut when an agency representative spotted him.

Since their debut in 2009, they have been at the top of their music ever since.

He has broadened his spectrum as an actor, making several movies and drama hits and being recognised by the public as an actor.

At some point, he hit a burnout. Everything was empty. He had insomnia and had many sleepless nights. He was close to collapse like this. After careful consideration, he decided to retire from the entertainment industry.

The night after his last concert, he passed away suddenly.

The media poured out speculative articles saying that it was an "extreme choice because of insomnia and depression," shocking the entire nation.

But was his death really a suicide?

Im Sol

A cute and lovable lady, she dreamed of becoming a film director. However, because of an unfortunate accident 15 years ago, she became a paraplegic, forcing her to give up her dream.

When she found out she would never walk again, she considered ending her life. She wished the morning would never come whenever she closed her eyes at night. On the day of the solar eclipse in 2009, she received a phone call at her lowest. The radio softly plays in the background as she answers the call in the hospital room. A man whose name she didn't know told her this:

Thank you… for being alive. It's a relief that you're alive. The ones by your side… will say thank you for that. So… live today because it's nice outside. I hear it's going to rain tomorrow. Then… while waiting for the rain to stop… try to live again. Then, someday… a day might come when living doesn't feel so bad.

At the end of his words, his soothing singing soaked her heart. It was the first comfort in her heart since the accident. She became an ardent fan from that day and followed the band Eclipse, for whom he was the lead vocalist. His voice was her firm support. Despite despair, she found strength in his advice and persevered.

Presently, Sol works part-time as a YouTube video editor and is trying to become a film editor. However, she faces rejection when she applies for an internship because of her disability. Despite her challenges, she remains optimistic, believing she will shine alone one day.

When she hears the noise of Sun-Jae's passing, her heart breaks again. At that moment, Sol's world collapsed. While heading to the hospital, she falls through time to 2008, before her accident.

She becomes determined to save Sun-Jae and herself, but will she be able to change her destiny miraculously in the time allotted?

Kim Tae-Sung

When Myspace visitors determined popularity, he was the ultimate ruler. In 2008, Tae-Sung was the bassist for the band Eclipse. A heartthrob with a flamboyant look. He is a big flirt who turns heads wherever he goes. He is in a band because he enjoys the attention of his fans and females.

Tae-Sung lives with his father, who is a detective. There was a time when he idolised his father, a detective who beat up bad guys. His father has always prioritised work above all else. Eventually, his mum left. He blames his dad for his mum leaving. He resents it, and that is the main reason for his rebellion.

The day after shy Sol confesses to him as other girls have done, she starts nagging him like an old lady, as if she had become a different person overnight. Is she just trying to get his attention? She is different and amuses him, and he is interested in knowing her more.

Will he accept her confession?

Baek In-hyuk

In-hyuk is a friendly guy who is the guitarist and leader of the band Eclipse and Sun-Jae's best friend.

When In-hyuk was sixteen, he left his hometown of the seaside village with a guitar and moved to Seoul, dreaming of becoming a Korean Bon Jovi. The first friend he met in an unfamiliar Seoul was Sun-Jae, and they became like family.

When a famous agency told him he was planning to form an idol band group, he rushed to audition and was lucky to be selected.

In the present day, In-hyuk and Sun-Jae are not on good terms. He feels betrayed by Sun-Jae's retirement announcement, saying he hasn't heard from him and doesn't know why. Their last encounter happened during a heated argument on concert day.

Sun-Jae, who only knows sports, seems like a kid who knows nothing about the world, so In-hyuk tries to coach him on everything. In reality, In-hyuk is just a music-obsessed idiot. So, if you observe them from afar, it's a case of the blind leading the blind.

Still, In-hyuk is ready to drop everything for his friend anytime, anywhere. But one day, a girl named Im Sol appears and seems to confuse Sun-Jae's mind, so In-hyuk is on high alert.

People around Sol

Park Bok-Soon

With the rent from a small three-storey building, she supports her two children and lives with her elderly mother. The first-floor gold video and DVD store is at risk of closing.

Ten years ago, she lost her husband in an accident and raised her young children, and her life became stronger and stronger. When her children are upset, sometimes they lash out without thinking. Deep down, they are sad that they are growing up without a father.

Jung Mal-Ja

A warm-hearted and wise grandmother of Sol. In the present day, she seems to have dementia.

Im Geum

Sol's older brother is an aspiring actor passionate about acting but repeatedly faces rejection in auditions.

He took a leave of absence from the university he was attending, smuggled tuition money, and enrolled in an acting school. He attends an acting school but continuously faces rejection in auditions.

After Sol's accident, he gives up his dream and takes a regular job. To escape the harsh life of working tirelessly, he ventured into stocks. However, this only led to a disastrous outcome. It doesn't look like he will get married in this lifetime.

Lee Hyun-Joo

Sol's best friend is bold, sharp, and sassy. She looks out for Sol and even adapts her car so she can drive her.

People around Sun-Jae

Ryu Geun-Deok

Sun-Jae's father and the owner of the Galbit House. A long time ago, he lost his wife to cancer and raised Sun-Jae alone. His son Sun-Jae, who started swimming and has been attracting attention by winning various competition awards, is immensely proud of him.

CEO Kim

He is the CEO of Sun-Jae's agency, JNT. He successfully debuted the group Eclipse and brought them to the top of the charts. After establishing JNT, he visited various schools every day to discover gems.

Park Dong-Suk

Sun-Jae's manager.

Kim Hyung-Gu

A Jagam High School swimming club member and self-proclaimed rival of Sun-Jae.

Choi Hyun-Gu

Sun-Jae's friend from Jagam High School's swimming team.

Coach Ahn

Coach of the Jagam High School swimming team.

Hyun-Soo

The drummer of the band Eclipse.

Jay

A bassist and the youngest member of the band, Eclipse.

People around Tae-Sung

Detective Kim

Tae-Sung's father is a 20-year veteran detective with a pleasant nature. He will be in charge of investigating the murder case of the Juyang Reservoir. Work always came before family. Unable to endure this, his wife went abroad after the divorce, leaving only his son, Tae-Sung, who had just entered puberty. After that, his relationship with Tae-Sung became strained. He is always worried about his son, who just goes astray.

Cha Yi-Seul

Tae-Sung's friend has a weathered appearance that belies his pretty name.

Choi Ga-Hyun

Tae-Sung's ex-girlfriend and they dated for about a month, and she hasn't forgotten him yet.

Nice detailed character explanation and their characteristics.