Its special star shape, indescribable taste and reddish colour don't really suggest its alchemical effects. However, it does have some : the ability to change into a Kitsune, with its animal and human forms. However, whatever you do, kitsune is invariably feminine. The maximum amount of testosterone possible enables a hermaphrodite stage to be reached, but with predominantly female characteristics.
One last thing I'll add to this experience is that natural kitsune can have nine tails, depending on their power. On the other hand, consumers of the fruit, however powerful they may have been before their transformation, never reach that number. The loss of magical power following transformation is a detail that I have to sort out, but I have to admit that it's only a minor inconvenience that has never caused any more problems than that.

The red starfruit is the result of many years of research, and was even one of my first experiments. It didn't exist in these parts before I arrived, but natural kitsune did. It was when I listened distractedly to a mortal talking about his love for one of these cunning females that I had the idea of... make his wish come true.
Using the essence of his sweetheart and combining it with a plant species that could receive the arcane, I managed to create a fruit that was particularly useful for lovers of vulpes. Unfortunately, while the kitsune had not aged a day, her lover was at the end of his life when I brought him the fruit. It was only a minor setback, however, as he took on features similar to those of his sweetheart, giving him a new lease on life in the process. The last I heard, these two charming ladies were living out their days peacefully in remote regions.