From 12, to 12

Chen Yuan had just turned 22 at his last year at in college. After visiting his childhood-friend's grandmother at a hospital, he receives a 2 page letter from her.
That night when he sleeps, he traveled back in time during the Second Sino War in 1937. While lost, he met a young lady freezing and dying because of her injury. It turns out that she was a Japanese soldier, or is she?
As they spend time together starting from enemies, they slowly fell in love with each other.

Later, he will wake up in the morning back to his own time and each night he sleeps, he will go back in time again, or did he really go back in time?
By doing this, he will find out mysterious and painful truths.

A love story born from the inside out, but split between two worlds and with many difficulties.
How will this love end?