Hollow Realization takes place in Sword Art: Origin, a restoration of Aincrad titled Ainground, with intentions of research and development in the year 2026, three years after the original Sword Art Online event. However, unlike in Sword Art Online, Ainground is one large floor, instead of multiple, while the castle itself was renamed to Aincrad, where several monsters can be battled.

The main character of the game is a 14-year old AI, known as Premiere, that travels with Kirito. Although she is part of the game's initial release, a later patch would tweak her "vocabulary and personality" in-game to a "specific character", based on keywords in Twitter tweets as part of a promotional campaign featuring the character. These conversations with Twitter users would dictate her personality over time and ultimately decide if she would become a "good girl" or "bad girl" in-game.

Other prominent characters from the franchise such as Asuna, Leafa, Sinon, Lisbeth and Silica also feature.

Links:

• Author’s Twitter
• Manga Artist's Twitter
• Mangaka’s Pixiv