Kimono Dragons

From back cover:
Nearly four years after a global plague killed every male mammal on Earth, the two exceptions -- Yorick Brown and his monkey Ampersand -- now find themselves in Japan. Following Ampersand's abduction by a sword-wielding mercenary, Yorick and his companions (government operative 355 and biochemist Dr. Allison Mann) have tracked him to the Land of the Rising Sun, where the culture has adapted to the loss of its men in some uniquely Japanese ways. To retrieve his pet -- whose body may hold the key to humanity's survival -- Yorick and 355 must travel to Tokyo and navigate a tricky maze of Yakuza remnants, little-girl gangsters and pop star entitlement gone mad.
At the same time, Dr. Mann and her new girlfriend head to her mother's home for a chilly family reunion. Their reception is even more hostile than expected, but it also results in a startling revelation -- one which could point the way towards solving the final, overriding mystery of what -- or who -- caused the Gendercide.