Sword Art Online Progressive: Scherzo of Deep Night

Synopsis

This may be a game, but it's not something you play. The world's first VRMMORPG (Sword Art Online) became a game of death. Over a month has passed since 10,000 users were trapped inside the game world. Asuna, who cleared the first floor of the floating iron castle of Aincrad, joined up with Kirito and continued her journey to reach the top floor. With the support of female Information Broker Argo, clearing the floors seemed to be progressing smoothly, but… Conflict erupts between two major guilds who should be working together – the top player groups ALS (the Aincrad Liberation Squad) and DKB (the Dragon Knights Brigade). And meanwhile, behind the scenes exists a mysterious figure pulling the strings…. In a dangerous battle of death, there is an assault that differs from the threat, and it will involve Asuna and Kirito…! (Source: Aniplex)

Synopsis via AniList.