Tekken's Unique Mix Of Mostly Real-Life Martial Arts Moves VS. Its Science Fiction Setting
Tekken didn't immediately click with me during the earlier days due to its non-projectile based gameplay mixed with science fiction. I always felt it was inconsistent through and through. While most of Tekken's moves are actually based on real-life martial arts, close combat style similar to Virtua Fighter (which came first), but Tekken still keeps itself consistent with the sci-fi theme even in the first game.
Think about it that even in the first Tekken game you really get some unrealistic characters like Kuma would probably kill Heihachi in real life, Jack and P-Jack are robots and "Devil" was an alternate costume for Kazuya in the console version. So I guess Tekken as a fighting game took the direction of mixing science fiction plotline with mostly realistic fighting game moves set to some very weird physics in some areas of gameplay.
The more Tekken progressed, the more the fighting still remains more or less the same except with smoother controls and easier to do combos and special moves. While most characters still used some realistic moves but characters with unspammable non-realistic moves like Devil's laser beam still continued to exist. The Mishimas even in the first game tend to generate electricity in their fists for some unknown reason.
Tekken's further travel into the realm of science fiction and the supernatural didn't just stop with androids and the Devil/Angel personalities within Kazuya. By Tekken 3, Ogre appears as the first monster type boss as Devil may be merely Kazuya's alternate form and personality. Tekken 5 would later turn Jinpachi Mishima into a vengeful ghost. In Tekken 6, Azazel exists as the first incredibly huge and difficult fighting boss to defeat with a supernatural origin.
While Tekken still remains with mostly real-life martial arts moves and non-projectile gameplay but it'll always remain in the genres of science fiction and supernatural in terms of story writing. I guess it also showed you don't need fighters with supernatural powers like fireballs to really write science fiction. After all, many characters in the realm of science fiction and supernatural do not possess such powers except for a few. I guess that's what gives Tekken its charm.