Gun Gale Online:Erebus

Kayaba Akihiko once dreamed of actualizing a world of swords, a floating castle, a fictional fantasy. But people change and Kayaba is no exception. Players welcome to Gun Gale Online where guns rule supreme and swords are obsolete... well unless you're Kirito that is. KiritoxSinonxHarem

An alternate reality where instead of SAO it was GGO that was released as the first VRMMORPG.