The Costume(no.1) is a very rare, very hard to make, and very powerful costume with strange powers. Only 5 are known to exist, and the only recovered one is in the hands (or paws) of Haru Samazanba Axeman.
A snow-white, bluish tinged, slightly feminine tight-fitting fluffy fox costume with a large, thick tail. Oddly enough, no makeup is needed, wearing it for 12 seconds is enough.
Haru confesses that it is a new one, he had to recharge it by trapping rare silver foxes, which, due to his low-level hunter skill, was quite a challenge, some of his hair, a bit of runite for the claws, some white feathers, and then dipping it in the Tears of Guthix, along with using some Serenity Crystals. A highly unstable costume just like it can be made from the spell Extract Morphing
The full extent of its powers is not known, but it is known that it has the power to turn the wearer into a fox. No ordinary one, either, with Haru he can make it sprout 8 more tails. This is also similar to something he can do in his power form. It is also known that it can turn the wearer into a kitsune (a fox that can turn into a beautiful woman) wearing something you only should see in magical girl anime. Haru has not used this for obvious reasons, because he claims the costume would not want him to. but if it is sentient, then it has fun driving the item hunters that steal it crazy, and mutating them.
It is true that the spell Extract Morphing offered a good way to produce powerful items like this, creating truly interesting warriors and powers during the God Wars and other notable battles, but, as the page on Extract Morphing says, "Accidents ranging from hilarious to deadly serious were prone to happening."
Another theory claims that it was part of a repopulation effort by an alien race