They probably added this because at some point the leads actually thought they were siblings. This tag sure was misleading, the whole time I actually thought they'd turn out to be real siblings.
they just made a remake leaving all of the best points/parts of the original. It's hard to believe that original was made in 2000 and this in 2016 and still 2016 one seems more stereotypical and outdated.
Felt like they were jumping from one incident to another. A poor manga adaptation it is.