Think out loud with me...
VIRUS: The "virus" was obviously symbolic of a guilty concience. When it escaped from its bed after infecting the first nurse was symbolic of the doctors and nurses really realizing what they'd done. It was them losing control of their guilt, and no longer being able to hide/contain it. They were forced to "study it". They were all clearly experiencing the hallucinations and the pain of losing their minds over it, but there was obviously something besides just guilt that made them all experience the same things, and all be able to observe the same things happening to one another.
AKAI: Who is Akai?? He can't have been the burn victim because although Akai sees his eyes through the bandages, and reads his name on the tag... that can only make sense figuratively. When Akiba is in the place of the burn victim, he sees Akai in the back of the room giving the wrong command (chlorate vs chloride) If Akai were really the burn victim, he wouldn't have been a ghost yet at that point, and he certainly wouldn't give a command to end his life. Plus, when Akiba flashes back to the malpractice incident, there is no nametag. So who is Akai? All of the other doctors and the nurses all recognized him as a doctor, even if he was a hallucination. He was obviously dead, because the old woman saw him in her mirror. If he had been a doctor at the hospital, the others should have been more shocked at his presence because they'd have known that he was dead. Maybe he was a personification of the guilt (virus) that consumed them, because he was constantly indirectly reminding them of their wrongdoing.
AKIBA: Akiba obviously was not consumed by his guilt until the very end when he realized that he'd killed all the nurses and the other doctor. But they all were consumed by their own guilt over the course of the night, so did Akiba just finish them off? Akiba was dead in the locker at the end... just OOZING with guilt. But why did he see himself as Akai in the mirror?
FEMALE DOCTOR: The doctor who discovers Akai talking to his reflection and the gruesome murders he'd commited was also consumed by guilt in the end too. There is no way she could have known what symptoms the "virus" from the previous night had, so she'd obviously done something worthy of infecting her with the same particular symptoms. What would be the source of her guilt? We never see her do anything worth regreting... BUT... I think she killed Akiba. I don't know what reason she'd have for it, but he was dead in a locker in the end. He obviously suffered from the virus, but someone had to finish him off and put him there.
SWINGS: I've read interpretations of the swings being moved by the ghost of Akai and Akiba at the very end. I suppose that's valid, but there needs to be more to it. Why would Akai haunt the hospital in the first place? Why would Akiba join him??
FOX BOY AND MIRROR LADY: I think everyone is trying to fit them too deeply into the plot. The boy was just seeing everything happen through his mask which symbolizes something (fear? pain? honesty?) The woman was just there to be creepy and give us an excuse to believe that there were ghosts. She gave us a way to see Akai at the end. She also witnessed everything, but was unaware due to her condition.
Any thoughts, comments, or help would be lovely... I'd love to discuss this movie with people!! I only know one other person who's seen it, and we're in agreement with everything we've figured out, but both ended up with the same questions. Think with me people!!! Message boards are beautiful things!