Naifanchi (ナイファンチ) is also called/pronounced Naihanchi (ナイハンチ) and in Shotokan the name and kata embusen (pattern) was changed by Funakoshi to  Tekki (鉄騎) as a derivative of the Okinawan Naifanchin. The name Tekki itself translates to "Iron Horse."

As a short and symmetrical kata, it is, depending on the style, typically taught between 5th Kyu and 2nd kyu to students of karate. Despite its simple and short form, the bunkai that can be applied to this kata from the feet up is vast. Hence while kyu ranks may "learn" it, the kata offers extended bunkai henka (alternates) that is usually re-visited for Dan ranks to extended knowledge.

In a few styles and in Shotokan in particular, there are three modern kata derived from this (Shodan, Nidan and Sandan). Some researchers believe Nidan and Sandan were created by Anko Itosu, but others believe that it was originally one kata broken into three separate parts (probably due to constraints of space). The fact that only Naihanchi/Tekki Shodan has a formal opening suggests the kata was split.

The karate kata is somewhat unique in that it is entirely performed in a straddle or horse stance often called naihanchi-dachi or more correctly  kiba-dachi (騎馬立ち).  One translation of the kata name is 'internal divided conflict'. The form makes use of close in-fighting techniques combined with whole body movement (tai sabaki) and grappling. However, while the kata movies side to side, the techniques can be applied against attackers at any angle.

For the Himeji derived line of Shito-ryu, this kata and an all shikodachi containing kata named Juni no Kata Sanban are the primary focus for 6th and 5th Kyu. These kata's low stances are aim ed at building up the balance, strength and a low center of gravity to further a strong base and body shifting - the emphasis at this ranks aligns with the fact that it is at this rank that historically sparring begins (sparring begins at this rank for the assumption that students have now been training long enough to exhibit correct technique trajectories so kumite technique does not begin with bad instinctual habits and an understanding of maai [distance] has been well drilled via ippon kumite). 

Itosu, a Shotokan and Shito-ryu lineage sensei by nature of being both a teacher of Funakoshi and Mabuni,  is reported to have learned the kata from Sokon Matsumura.  The oldest known reference to Naihanchi are in the books of Motobu Choki. He states the kata was imported from China, but is no longer practiced there. Motobu learned the kata from Sokon Matsumura, Sakuma Pechin, Anko Itosu and Kosaku Matsumora.