Sword Art Online Progressive 7 (light novel) — Reki Kawahara

LUCK BE A LADY TONIGHT! The seventh floor of Aincrad-a massive casino where over half the game's beta testers dropped out before launch. Kirito was among the many who lost everything in its Battle Arena back then. When an informant named Argo the Rat entices Kirito and Asuna with knowledge that could aid in their investigation, the pair soon plunge into the casino's dark underbelly once more. Meanwhile, the “Elf War” quest also reaches a sudden turning point when a flurry of crises rock the dark elves' home!