によって and passive question > > > > **** > > The fantranslation says: > Natural healing that regenerates the wounds Saber sustains. But isn't Saber the one who hurts Rider and Rider the one whose body is being regenerated? Can someone explain?

The fan translation is not correct and your intuition is. The passive indicates the "agent" of the action by (whether is added or not is a different topic). So what it should really be is

> Natural healing that heals (Rider's) body who was injured **by** Saber.

So the lesson is don't always trust fan translations.