In Sword Art Online (season 1) episode 9, at about 16:00, someone with blue hair woke up Kirito. When he regains consciousness, it was Asuna. But she doesn't have blue hair!
Here are some pictures.
This was just before he woke up:
Then:
What's going on here?
That would be Sachi. She's umm.. you know. big spoiler. As you can see from this screen shot, her hair is blue.
The face and the hair colour of the girl trying to wake him up looks similar to Sachi, the girl from the guild of which Kirito was the member long time before this scene.
I'm pretty sure this is Sachi and not Suguha because of two reasons. Firstly, at that moment, Kirito wanted to be apart from Suguha because he found out the family he lived with was not his real family (I mean not his true parents and Suguha was not his sibling) since the age of 10. Secondly, Kirito joined that battle (the scene before your illustrations) because he did not want any friends and guild members ended up disappearing in front of him like the death of the "Moonlit Black Cats" of which Sachi is the member, so maybe he saw the blue haired girl due to his guilty feeling.
It is definitely Sachi. This is evidenced by the mole just below her right eye.
In your image, the mole appears in roughly the same spot.
This is also backed up by the fact that, at the time of this particular scene being shown, out of all of the other female characters introduced - that being Lisbeth, Asuna, and Silica - none of them have a mole on their face. The only other one that could come close would be Lisbeth, but she has freckles on her face.
I believe it may have been Suguha over Sachi. if we look at a younger image of Suguha we see she has Blue-ish hair
also Sachi's sidebangs are longer going past her chin
while with Suguha, despite the fact in the image bellow they are behind her ears we can guess her hair length of these side bangs to when she was young (in the previous image they are the bang just before the flower clip) and probably isn't nearly as long as Sachi's
Also the fact the they are trying to wake Kirito up makes more sense that it is Suguha as she would be wanting Kirito to wake up, maybe some sort of feed from reality. there isn't much reason for Sachi, or her ghost, to be wanting Kirito to wake up so urgently while with Suguha, someone she loves is still almost wasting away in a coma like state.
I had always thought that it was Sugu, Kazuto's sister. That, somehow, Kirito briefly glimpsed the real world. But, in retrospect, it was Asuna.
Firstly, it cannot be Sachi: Sachi is dead, and other than the strange occurrence of Griselda's brief appearance, the dead do not reappear. If Asuna hadn't seen had Griselda, too, then I would be apt to think that this was a hallucination. For now I will call it an anomaly or glitch in the system. I am sure there could be many considering Yui, Asuna defying paralysis, and Kayuba's surprise when Kirito refused to die before issuing the fatal blow, just to name a few.
As I said above, the first time I saw the episode and the black-haired girl, I was certain it was Sugu. I thought that Kayuba had lied and you didn't really die when your HP hit zero, he had just said that to give a more realistic and final feel to the game so that the players would take it more seriously. After Kirito finished it and Kayuba confirmed that everyone who had died in-game was really dead, episode 9 left me confused. How had Kirito then been able to see his sister?
Had Kirito, being so near to death, briefly viewed his sister crying over him in the hospital? But, then, why would she call him 'Kirito'? She did not know him by that name. In fact, based on her reception of Kirito in Alfheim online, she had never heard the name before. So, why would Sugu be calling Kazuto by the name of his avatar? And why would she be using -kun if she knew she was addressing her brother? As the younger sister she would use the honorific -san or -sama, but not -kun. Understanding this he can only be hearing Asuna calling him, which is evident in the next blink when it is Asuna's face before him and not the black-haired girl. But, who was the black-haired girl and how had Kirito seen her in the first place?
Again, I can only fall back on the anomaly or glitch in the system theory and well as the strength of Kirito's own character. Only someone of extraordinary strength of character would have the capability of defying the system. Yui was attracted to both Kirito and Asuna because something about them was different from every other player in the game. Was it their love? Their strength? Their life-force? Something within their character is strong and Yui sensed it. And, as previously mentioned, Asuna also showed an anomalous ability by defying paralysis in order to protect Kirito. Was this strength enough to bypass the systems parameters so that in a near death experience Kirito could momentarily glimpse the real world and see his sister? Yes, I think it was.
But, as to who woke up Kirito - while I think he may have glimpsed Sugu, I belive he was still hearing Asuna for the reasons mentioned above, and that it was Asuna that actually woke him up.
