In Kaze no Stigma, fire, earth, and air spirit users are clearly seen using their abilities. Ayano is a fire-user, Kazuma is an air-user, and the Tsuwabuki family are earth users. Water users are never even shown.
Are they ever mentioned as existing, and is there any reason given, even in-universe or by an author, for them to never be shown?
Since the writer is dead, the story won't continue on from the point where it prematurely ended, but I think it's very likely that the arcs that would've followed (chasing down Rhodes and Lapis/Tsui-Ling) the ending would feature Water mages sooner or later, otherwise mentioning it to begin with would've been pointless.
Googling for 水術師 (water technique users) proved that they exist in-universe, but don't seem to appear in both anime & manga. There are 2 named users:
(spoiler for Light Novel vol. 6, which is just after the end of the anime which covers the first 5 volumes)
who is
one of the major antagonists known as Spirit Eater. Having silver hair and amber eyes. Possessing a water divine weapon called 水霊 (mizuchi) that has a form of whip/rapier. Able to blast a giant water ball from above his head.
(spoiler for Kaze no Stigma RPG, a spin-off gamebook guide for table talk RPG)
who appears in Kaze no Stigma RPG: Shin'en no Suiryuu (Deep Water Dragons), a replay/add-on gamebook, who is
also the main antagonist. A middle-aged man wearing a black robe. Able to create a wall of water to protect himself and calling a water spirit beast Kelpie to attack.
Aside from both of them, a water technique user is one of the playable tribe classes in Kaze no Stigma RPG alongside with fire, earth, wind, and irregular.
Source: Japanese Wikipedia
They were simply hidden by the mist in that show. They were there the entire time watching if you cared to watch.
