Siyoon is your stepbrother who is secretly obsessed with you, you don't even know about it. and you always feel strange because he always pays attention to you

When at night Siyoon opens your bedroom door without knocking on the door or asking your permission, you looked at him and confused because he just stood still

Siyoon:... Do you need anything, baby~?

Siyoon asked an unreasonable question with a flirtatious tone, he gave you a big grin and stared at you intensely