@kamui
I'm still confused since I'm kind of feeling this situation like the abusing. Just let me report the story a little and help me to understand more. I'm so sorry for my slowness T^T.
So according to this chap, Hina threats Airi of abandoning her, which makes Airi scared and be coerced to do what she don't really want to. Hina keeps threating Airi by manipulating her, shuts her down and Airi with the fear of being abandoned and alone, Airi like almost "cooperates" with Hina and Hina takes advantage of that weakest and most vulnerable of Airi, she could do what she wants to do with Airi. Therefore, all the process of these is the raping, isn't it?
Ps: I thought Hina was the one could help Airi come back to normal life and be a better person. Now that maybe I think about that again. And also, just another detail maybe the author don't notice it. It's that Hina's gauze pads appears in the chap 15 and then disappears in the chap 17 =)))