Yeah.. that's possible.. maybe died in the accident with the mother
Actually ru ha said a few panels after that he didn't remember 'what they did on that hill'
So he didn't remember for sure if she was actually a boy
So that person ru ha Perf with could have actually been a boy, or could have been her
I think that she might be his twin sister, since they talked about her so much and the title is even 'ruby Doll' = doll = sister, so the sister has an important role, so it's the MC, and she looked at the doll that represents her sister and feels a bit touched and all
But then, that would be incest with ru ha and I don't think the author would do that so i'm not sure...
have someone read the raws? Is Ru Jin, Ru Ha's twin sister. I mean, Ru Ha remembers little Ru Jin to be a boy who he plays "who can pee the farthest". you can't possible fake that.