I disagree with Fuu, I have a strong feeling that she's the one behind all this, I mean, think about it, who else knows Uichi so well, besides that if she talks and gives advice to Uichi's sister then she probably knows about games and technology, something that Fuu knows very well, she barely appears and hardly helps with anything, she never talks to Uichi even though she knows what he's going through (at least it doesn't show that she talked to him). I have a theory that in the original timeline something happened between Fuu and Uichi, maybe she liked him or Yotsuba but could never be with either of them since they love each other, it's a big maybe, but I don't know, it makes sense to me.