Can someone pls summarize from the start (￣∇￣")

Same I forgot everything

Nothing happened to summarize

From what I remember

•Byul has a new sister
•Byul was a trainee
•Byul secretly visits his Grandmother
•Byul is ahh at school so he had Siwoo help him to score high in his class Siwoo and Byul use to be friends

That’s all I remember

What's the girls relation to him again? I forgor