Sachi seems more and more like a heterosexual to me. And it's not because she had a boyfriend in the past (she could still be bisexual or even lesbian, because she was just confused), but because she somehow seems really cold towards Ruki - there is no passion from her at all, she actually kinda reminds me of my ex, who was also het, but somehow went with the flow with me (I have some nice memories, but in the end it was a complete disaster :D). Also asexual people exist and are not even so rare, but I don't think, it is possible for an asexual person to have a relationship with someone who is hypersexual. An asexual person and ordinary person- they can probably compromise, but in Asuna and Fue's case it's just impossible.