Who says it’s either Tsukasa or Amane? Judging from the age, it could be the house fucking with them, but it could be a little sibling of both of them. The age doesn’t line up at all to when Amane/Tsukasa died, and the personality (from what I can see) isn’t like Amane OR Tsukasa, though it is leaning more towards Tsukasa. But hey, then again I can be one of them, but keep in mind this manga artist/writer likes playing with our feelings and I wouldn’t be surprised if it’s a younger sibling to the two. In fact that could have some explanation as to why Tsukasa is so attached to Amane.
Welcome to Spain without the S... ┗( T﹏T )┛