What does Unohana Retsu's Bankai do? What does Unohana Retsu's Bankai do?

It was not so clear in the manga.
As for all the information that is currently available


  she finally enables her Bankai! Blood spills from the skies, as though it was rain, she enables it caller her Minazuki Bankai out! Zaraki notices all the blood that’s dropping! Unohana’s sword is straightened and changes into a sword with never-ending blood oozing from it. She mentions that the play is over!
  Both of them go crazy and quickly go on their attacks! They keep on clashing, Zaraki can feel that the sword Unohana currently has melts her, it starts to degrade his face from skin to flesh and to bone! He mentions that it’s fun! He notices his hands and cloths degrade away from his bony hands. He asks himself what that is, he mentions that everything seems to be different, at the same time, he sees Unohana with no face except bones!
  Zaraki mentions that everything is so different, he’s been asleep, he’s  just been dreaming about their contacts over and over again, he calls this exchange to have no name, but thanks to her, she now realizes that this can be called, Fighting! They keep on clashing swords and spilling blood! Unohana mentions that she likes fighting! Zaraki likes it so much that he can’t help it, Zaraki is back to seeing flesh and blood again. Source


It seems like a weird kind of bankai to me very Illusive