Sword Art Online Progressive 5 (light novel) — Reki Kawahara

After successfully untangling themselves from a dangerous encounter with the Black Poncho Man and clearing the fifth floor of Aincrad, Kirito and Asuna head to the next challenge, an area filled with...puzzles?

What's more, because of the precarious balance of power between two large guilds aiming for the same item, "The Flag of Valor", there's also a murderous PK group to be wary of.
As the problems seem to pile up, Kirito and Asuna face the sixth floor of Aincrad completely unaware of the malicious trap awaiting them!!