The side-hair girl refers to a girl whose name needs to be known.

She has a conspicuous hairstyle of pointy black hair tied at the top and to the side.

Her bust size is given in an earlier chapter when everyone has physicals.

She is smaller chested than Na-Young.

In chapter 40 after Na-Young clears Kang Han-Gyul from suspicion and he has bug on his face, she has a thought bubble of "he's smiling..."coming from her.