It is very deliberately that Knives has kept himself closed off for a long time, from the song of his sisters or even the potential reach of his brother. Temptation was a terrible thing, and he saw no need to invite it in.

Except there was this much younger, healthier version of his brother. Foolish and full of dreams not yet completely brought to ruin, likely to run into trouble sooner rather than later. And so he's kept a bit of attention out, a cautious feeler extended just in case; the brother that shared a timeline with him would never call out, but this one .. this one very well might, out of loneliness or fear, or running afoul of the Terrans or more. It's a good thing he is, it seems, by the strained call that he picks up on eventually.

Not Vash's pain. 'She'. Who is she? Why is he so afraid for her?

You're not a bother yet. Are you safe? Who is 'she'?