[natsu_san]

Originally Posted by Alucard24

I would like to ask a simple question : Why heathcliff won ? It seems even Kirito was surprised but strangely, he didn't investigate this....

If you don't want to get spoilered don't read this !!!

Spoiler for You have been warned:

The truth is that Heathcliff is no one else than the GM of SAO, named Kayaba Akihiko.

Spoiler for How he discovers it:

Kirito discovers his true identityy after the fight with the 75th floor boss ended. Seeing Heathcliff's HP's didn't go below 50%, Kirito is very surpised and attacks him, revealing his "Immortal object" status. The reason why Heathcliff's HP didn't go below 50%, his speed which exceeded that of the system and the fact that he knew all of Kirito's skils is proff of his GM status.

Spoiler for End of SAO spoiler:

Nevertheless, Kirito manages to finish him off after their fair duel in which Heathcliff disregards his "Immortal Object" status and lowers his HPs to the same level as Kirito.

Seeing Asuna save his life at the very last moment, die in his hands, becoming enraged and seeing his HP reach zero and being on the verge of death, he recalled Asuna's actions - who were paralyzed by Heathcliff, but managed to protect Kirito anyway - and he killed Heathcliff / Kayaba Akihiko, bringing SAO to the end.

Anyway the anime cuts many interesting parts - mostly descriptive - therefore most of the thoughs aren't there. In the anime Kirito is just shocked, while in the LN there are more details on his thoughs.