So, the leader of the Front, “Thinker”, is trapped deep inside a dungeon, a hidden dungeon underneath the First Floor. Along with a representative of the Front, Kirito, Asuna and Yui end up exploring this dungeon. I mean, I really like the Kirito and Asuna pairing at this point, because they’re so much like a couple, and they even act as a couple together. However…before long, we see just why “Thinker” has sat still for so long; in a hidden dungeon, there’s a hidden boss…and these hidden bosses are tougher than normal ones. When “Scan” doesn’t reveal any data about a boss, it’s clearly ridiculously powerful. Kirito and Asuna’s skills don’t come anywhere near blocking or even damaging this guy, so when Yui steps out in front of this boss and unleashes some rather strange abilities to OHKO this hidden boss…well, I can’t say I was surprised, since i’ve had a feeling about Yui from the very start, but those who didn’t know that she’s a hyped up NPC from “Cardinal”, the system running the world inside Sword Art Online.
A program designed to monitor the mental state of players, Yui eventually broke herself off from Cardinal to get close to Kirito and Asuna, the only two players who aren’t overcome with grief and despair on the inside. So Yui gets turned into an item by Kirito and they continue their journey through the world of SAO…a by-the-book episode, to be honest.