[Velden]

I don´t understand japanese. I only saw the images of the raws but

Spoiler for spoiler???:

it does seem that in the end Ayu was the sister. At least that sounds good because, considering the recent (translated) chapters, Mayu was the one who didn´t want to be the sister, while Ayu, on the contrary, didn´t want to lose the relationship as a sibling.