Subaru, we're twins. There's no way that anyone could ever replace you, and I hope that to you there's no one that could ever replace me. No matter how smart a computer may be, or how someone else may be, there's no way two people can be exactly the same. Everyone is unique and different, so someone can never truly be replaced. [Smiles softly.]
Which is why Subaru should get to go home, so he can help grandmother and so that he can live again to fulfill his dreams.