This is my opinion but I don't think this is BDSM or intentional assault/sexually harrassment. I think this was Astina's emotion explosion or how I call it. We have to realize that she had to kill theo her love with her own hands and it was probably horrible for her. I think she had to bottle up her emotions and everyday for her was probably hell. After seeing Theo's face after for so long it must've just been a sudden raise of anger to theo and her wanting answers and possibly guilt as well. I know what she did was wrong but I'm not mad at Astina just shocked at what she did and worried for theo. We're not informed on what exact relationship they had but we can clearly see that Astina really loved theo and he did the same. I can't really explain my point that well but I guess you get the jizz of it. I really like this manhwa since the story is interesting and different I would say, thre are clichés but I would say they executed it quite well
CH0K3 M3 L1K3 Y0U H4T3 M3 BUT Y0U L0V3 M3~