Given the little shit uses hypnosis then basically rapes her constantly, big sis is *very* right to be wary of him.
Well... yeah. To be fair, they both like each other a lot, they just both are really bad at expressing themselves, with Seo-yun enjoying being the bratty bitch friend of the relationship more often than not. That said, he definitely needs to find a way to tell her how he feels without resorting to phone-based mental manipulation. He doesn't even need it. She'd be down for him dicking her down good if he just asked.