Both has time travels, “death”, heartbreak and also first love. Except from languages, most of the descriptions sounded similir.
Someday or one day:
The year is 2019. The 27 year-old Huang Yu Xuan terribly misses her boyfriend Wang Quan Sheng, who has been missing for two years and is presumed dead. Her birthday wish for this year is to "see him."
Blue Birthday (My summary):
Oh Ha Rin’s birthday wish was that she wished her boyfriend didnt died on her birthday. Oh Ha Rin will revisit the past through mysterious photos left by her first love, Ji Seo Jun who died on Oh Ha Rin’s 18th birthday.
Blue birthday (actual detail):
A fantasy romance drama in which Oh Ha Rin will revisit the past through mysterious photos left by her first love, Ji Seo Jun who died on his birthday 10 years ago. He had resolved to confess to his childhood friend since elementary school but he ended up taking his own life, much to her shock and horror. He was about to confess to her when he met his sudden death in the photography room.