Sword Art Online 7 (light novel) - Reki Kawahara

Kirito and Sinon's battle with Death Gun is over, but mere weeks later, something strange is afoot in the next-generation VRMMO ALfheim Online. A new duelist with a custom sword skill is defeating all comers--including Kirito! But when Asuna goes to face this duelist, she receives something she never expected: An invitation to an exclusive guild! But what is their aim? The Mother's Rosary arc begins!