A katana is a Japanese single-edged sword, developed between the Heian era to the Edo era. A katana was forged by a sword smith who smelted Japanese sand iron, called Tamahagane, removing impurities by folding the blade over and over. Katana were known for being incredibly sharp and versatile weapons, though they have to be meticulously taken care of. Katanas were used by the samurai of ancient and feudal Japan.
The ancestor to the katana, the tachi, was a long cavalry sword worn edge down, accompanied by a shorter sword called the uchigatana, in a manner similar to the wearing of the daishō, the katana and the wakizashi.
In Mortal Kombat
The blind swordsman Kenshi wields the ancestral katana Sentō, possessed by his ancestors giving it incredible power. Although he has no formal training in Japanese swordsmanship, his ancestors guide him and give him strength to use it.
The vengeful ninja wraith Scorpion also makes use of a katana but called a "Ninja Sword" in MK: Deadly Alliance. However he changes his katana with a custom and proper Ninjato after practicing Mugai Ryu in MK: Deception and Armageddon.
Suchin, Kenshi's former lover and the mother of Takeda Takahashi. Makes use of a Katana when the Red Dragon goes after her and her son due to being related to the blind swordsman. She fended them off with her hidden katana until she died.