Synopsis :

Yunho and Selina, are both in College, Yunho as her sunbae, in his last year of college and Selina a sophomore. From Day 1, when Yunho saw Selina, he fell for her instantly and step by step, he started to approach her and in the end, they eventually got together. Yunho and Selina had planned major things together as they both promised each other to be together even if Yunho had graduated. Being a member of the Flower boys in School, Dbsk, It was hard for him first to date Selina due to all the girls that was giving her a hard time but eventually, they got through it and ended up being together.

Yunho has never ever loved anyone as much as he loved Selina and he knew that She's is his Soulmate. Therefore, he planned to marry her, but will not propose to her until he had graduated

Selina was feeling the same way for Yunho. Her first and last love, that'll only be Yunho.
A couple passionately in love and would even sacrifice each other's life for another
But until one day.. a few months before Yunho's graduation, both of them are being involved in a carcrash, A drunk driver, lost his control and hits Yunho's car on Selina's side

Selina passes away and Yunho is heartbroken and falls into depression, not willing to do anything

Even if Selina dies, her soul didn't since their band between them are way too strong.
Faith knows that both of them were meant to be, but the accident came across..

Faith shows her the Lake of Destiny, Showing what will happen to Yunho in the future.

Because of the caraccident, He blames himself and refuse to do anything, to eat, to drink and he locks himself up because of his depression, because of Selina's Death
In the end, The Lake of Destiny Shows Selina her biggest fear, Yunho will commit suicide

Selina is given another chance to be reborn into another body, a girl called Lee Yeon Hee / Yuki
If she manages to save Yunho from committing suicide within 100 days and make him realize that it's her.., She will be able to come back to him as herself, Park Sol Mi / Selina, to be with him again..

But there are rules :

1. She cannot tell anyone about what she's been through
2. She cannot ask for more time, the limit is 100 days
3. And Of Course, She cannot tell him or anyone else that She's Selina...

And so it all begins..