Something that will become clear next chapter so I did not worry much, but Fiadh can recharge vail from a distance. The less obscure fragments of his flashback show him doing that in secret with Immaculate's crystal.
can you hear that?
yes indeed, it's commentary time.
asha's rather justifiable tantrum puts in perspective his words at the start of the chapter, which helps fiadh become motivated and fighting for their lives instead of letting go again like in the cavern.