In 1995, perhaps to coincide with “Gamera the Guardian of the Universe”, publishing company Shogakukan released a bunkobon (small-format paperback book) entitled ”Gamera vs Phoenix”. Or Gamera vs Phoenix: Monster War of Love and Emotion” as it’s alternatively called (more on that later).

It was written by Nisan Takahashi, the scriptwriter of the Showa-era Gamera series. And may have been based off on a script that Takahashi had drafted for the one and only Ishirō Honda, to help start a new, but never realized film production.
All this information comes from very limited sources (links shared below), but considering that Gamera is no-where near as famous as Godzilla is, a lot of the non-movie, auxiliary elements of the former’s franchise remains largely unknown here in the United States.
On the other hand, the extended title of the book, ”Gamera vs Phoenix: Monster War of Love and Emotion”, might suggest why this book is so obscure - the story might be horrible!
I don’t mean to be negative, especially since I often defend Obscure Kaiju wherever they may appear. But that subtitle hints that the story might have been on the pretentious side. And this was mid-1990’s Japan after all, when such trends were in extreme vogue (hello Eva).
No clue on the story itself, but the cover image makes it clear that Gamera meets some kind of fiery bird entity, possibly equal to his own powers and abilities.
Gamera vs Phoenix” is long out-of-print, and all remaining copies are insanely expensive at that ($999 US). Which makes the this even all the more frustratingly unattainable.
Gamera Wiki Listing: http://gamera.wikia.com/wiki/Phoenix
Amazon Listing (link might not work, de to its length): http://www.amazon.com/Phoenix-Gamera-VS ... 920&sr=1-2