Tragic that they're discontinued... Some of the best fics I've read:

[M] Comet of 86 - buddy_molly

7 chapters: " An unexpected business trip brings Sana back to Korea. Of all the people in the bustling city of Seoul she runs into Kim Dahyun, the ex she hasn't seen in ten years. The ex who also happens to be her first love. This is a story of blooms and bursts across sea and time. A story of two women and a love that never really went away..."

Immaculate writing. Truly angsty. Breakup fic. Starts with unexpected reunion and dives into the beginning of their relationship all the way to their breakup. It hurts so much ;') (but it's soo good)

Available in AO3 and AsianFanfic

[M] Odd Cravings - impulsivesaidas

14 chapters: "There are three types of people, Humans, Vampires, and Vampire Hunters. Dahyun was unlucky enough to be a stray Vampire, Sana was diligent enough to hunt her down"

Really enjoyed the Saida dynamic in this fic. Mochaetzu as vampires is also very adorable. Funny too. A lot of potential. First vampire au I've read.

Available on AsianFanfic

[M] Blue - minatosatang

18 chapters (too long so I will summarize): Dahyun, a Twice member, deals with problems internally behind camera and Sana is always there to comfort her.

I loved the Saida dynamic in the beginning (it was so endearing) but then afterwards... Let's just say the last chapters leave you 0o0. ngl the last parts had me f