“Enbusen (演武線) (embusen) isn’t just about where you face when you perform kata. Enbusen is the opponent themselves. Enbusen represents the opponent’s attacks or movements, the practitioner must move accordingly to the movements of the opponent, and react to said attacks accordingly….. Enbusen is the opponent.” (End quote) – Toshihiro Oshiro 9th dan Shima-Ha Shorin Ryu
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When people say enbusen, they immediately think of the performance line of a kata. Enbusen is more than this. Many karate-ka also think that the kata must start and end at a precise location on the enbusen…. We are all different shapes and sizes, therefore this would not be possible for everyone to be as exact as everyone else….. There is so much more to the enbusen than this.
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‘Seichusen’ (正中線) in Japanese, is the ‘line of attack’ or ‘line of defense’. ‘Seichu’ in Japanese means ‘exact middle’. ‘Sen’ means ‘line’. It is the path that the opponent’s attack has to traverse in order to reach you. By the same token, it is the path that your attack must travel in order to reach your opponent. By defending your seichusen and attacking through his seichusen, it may be possible to overpower your opponent.
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Seichusen also has to do with body posture. Therefore the enbusen is much more than a performance line.
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Kata are much more than their ‘enbusen’. There’s a myriad of techniques, principles and details that you can’t see at the beginning. The real beauty in kata is that there’s ALWAYS more to it.
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If you have good pattern recognition skills (and you’re paying attention), the pattern of the kata are relatively straight forward to memorize, and walking through your kata may seem relatively easy…… But doing it right, not so much. 
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References from an interview with Toshihiro Oshiro and American Samurai Vol 7, July 2002
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