She has a Tower item that lets her see people's feelings. I forget what it's called but it seemed tied to the Tower system. Hajin hasn't explained himself to anyone. If anyone required an explanation, it was Nayun after Hajin killed Chae Jinyoon, but Hajin refused to say anything about it to her and only explained to Yeonha after she'd practically pieced 70% of the story together herself. He doesn't explain anything unless forced. Boss isn't exactly the sort of person who sits down and talks about her feelings either. I know a lot of people are on the BossxHajin ship, but seriously, Boss is almost as emotionally stunted as Nayun is and has extremely little curiosity about finding things out.