Chapter 3: https://www.asianfanfics.com/story/view/1445669/tape-where-it-all-began
tape's authors new account.

Chapter 3: Erm... i don't know if this is the right one but i know a story titled "Assisting Miss Bae" too.

It's about Seulgi having a brother... and her brother is girlfriend's with Joohyun, who happens to be Seulgi's teacher. It's on-going, but it updated just few days ago.

https://www.asianfanfics.com/story/view/1450341/assisting-miss-bae

Chapter 2: https://www.asianfanfics.com/story/view/1418811/you-smell-like-the-devil-but-you-feel-like-the-lord

Chapter 1: Kanggerbae's ' tape' and 'Harmony' are one of my fav stories too, but sadly the author already deactivated the acc so the story no longer exist :<