Sword Art Online Progressive, Vol. 6 (light novel) - Reki Kawahara

At long last, Kirito and Asuna have reunited with Kizmel the dark elf. But the happy reunion doesn't last for long. With remaining keys to collect, the appearance of AI that seem a little too lifelike, and a "secret quest" to deal with, Kirito and Asuna will have their hands full as they attempt to clear the sixth floor in one piece!