The hero's redhead is actually calm, at least most of the time.
Love Interests have always been Colour-Coded for Your Convenience.
Traditionally, the hero's significant other would usually be a blonde, to contrast with the brunette Vamp or Femme Fatale.
But today, the passive Damsel in Distress and Satellite Love Interest have been replaced by the sassy, bold, brash, sharp-tongued Action Girl and Well, Excuse Me, Princess!
— easily compatible with the "spunky Fiery Redhead" stereotype.
This may be that, unlike almost everywhere else, red hair is not really seen as especially "exotic" in Ireland and Irish made media reflects this.
There isn't always a reason for this; if there is, sometimes, the red hair is symbolic of love and romantic desire, or the author just finds girls that look like that appealing.
There are some cases where the redhead actually The Hero.
In European comics, the high proportion of redheads among the main protagonists has been explained by some authors by the simple fact that, since redheads are rare, they're easier to spot in the panels — especially true for crowd scenes.
Look out for the large number of Dark Skinned Redheads in Anime.