Ummm am I the only one who feels sorry for the ghost? It's a happy ending indeed. But I can't help thinking that the ghost is pitiful. Especially when he said (this is the world of the living, so..)
More like it was a spirit than an actual ghost, the spirit of an unconscious men who suffered a fall and was in the hospital. If the body woke up the spirit will go back to his original body, he didn't disappear it's the same person. But the only different is the memories the spirit had would disappear when returning to his original body.
Actually, I think that the "ghost" Mimori san saw was just a manifestation of the time he spent with Iku, as if it was there to show him that what Iku said was real and not science fiction. I don't think that "ghost" even exists outside of Mimori's head. It's only there to show that there is something in him that is drawn to Iku.
I'm huge fan of this mangaka! Their art, storyline and the characters they create are super amazing!!! I LOVED THIS MANGA. I LOVED EVERY SINGLE CHARACTER! but the ending is sooooo lame.. like daaamn you better have a sequel for us or something!! You need to fix our hearts since you are the one who broke them!!!! I HATE YOU!!! (but I would still sacrifice my soul for your happiness) damn yoooooou sensei :'(