Ikuto Hirose wrote that, with a "unique sound that fused heavy metal, hard rock, classical music and even kayōkyoku melodies, X Japan unlocked musical possibilities that transcended the boundaries of genre."^[1] Mamoru Gotō described X's sound as being rooted in "Helloween-esque power metal" and layered with elements of thrash metal, hardcore punk and kayōkyoku melodies.^[2] Kazuaki Nakatsuka wrote that their musical breadth features "fierce metal that obliterates everything in its path, beautiful and dramatic ballads that transport the listener to the very depths of emotion, and raw, raucous rock 'n' roll that compels the body to move."^[3] Nakatsuka opined that Toshi's high-pitched vocals, which he compared to those of Minoru Niihara and Genki Hitomi, are a defining part of the band's sound. He explained that in actuality, Toshi's pitch is not particularly high, but rather, his distinctive vocal timbre makes his voice feel higher to the listener than its actual vocal range.^[3]

Yoshiki cited the Sex Pistols, the Clash, GBH and Chaos UK as among his favorite bands.^[4]

Pata has cited Frehley, Rick Nielsen and Jimmy Page as his favorite guitarists.^[5] Heath cited Mötley Crüe, Deep Purple and Rainbow as influences.^[6] All five of them have cited Kiss as an influence.^[6]

Nakatsuka opined that what set X Japan apart from their predecessors in Japanese metal, such as Loudness and Vow Wow, was that those bands revered and imitated Western acts, whereas X shattered conventions, even in the face of criticism, thanks to their "one-of-a-kind metal sound, eccentric band image, and promotional strategies that defied common sense".^[8]

Gorō Iguchi presented an aesthetic that appeared utterly bizarre and otherworldly to every observer. "Psychedelic Violence Crime of Visual Shock" served as both the foundational bedrock of their music and their guiding principle for the future. This boundless energy naturally manifested itself on the live stage; from drumming characterized by relentless, high-speed barrages to vocals that soared with piercing intensity, every element exerted an extraordinarily overwhelming force that commanded the very space around them. and this spectacle of violence and beauty clashing and sublimating into something transcendent was utterly mesmerizing, leaving audiences captivated and enthralled.^[9]

Will Hodgkinson of The Times described X Japan as having, "the grandiosity of Queen, the heavy-metal hysteria of Iron Maiden and the symphonic sophistication of classical music, all tied up with a healthy dose of melodrama."^[10]

Music journalist Showgun Fuyu cited Yoshiki as the pioneer of onnagata band members in visual kei.^[11]

X Japan's appearance was inspired by glam rock, Kiss, David Bowie, as well as traditional Japanese kabuki theater, where it is customary for male actors to play female roles and dress like women. Visual kei artists still often employ feminine looks and garbs for their stage.^{[12][13][14][7]}

According to Josephine Yun, "like its music, X's look was individualistic. Square-shouldered Toshi donned leather and metal, looking like a character out of the anime Gundam. Taiji dolled up in perfect, pretty glam. Pata's sleepy, backseat demeanor and whiskey bottle became his trademark, as Hide forever goaded the audience. And Yoshiki was a paradox all his own, bewitchingly effeminate one moment—and a full-force, wrist-breaking (literally) hurricane in concert the next."^[13]

Yoshiki's highly androgynous looks, dressed in lace and pearls, were referred to as "decadent". The band also used accessories reminiscent of glam-goth (metal jewelry, crosses). Their stage reflected the band's duality in nature: the forceful, "masculine" heavy metal songs were balanced out by Toshi's high-pitched tenor voice and Yoshiki's soft piano playing, where he would often wear long female dresses, and act effeminate.^[14]

By the time of their 1996 studio album Dahlia, X Japan had toned down their "dark" stage appearance, cutting their hair and wearing more rock-inspired outfits.^[14] In a 2010 interview, Yoshiki stated that the abandoning of stronger make-up and outrageous outfits was a natural progression in their style; however, they still used make-up on stage, "sometimes heavy, sometimes less", and that he still considered the band visual kei.^[15]