Seigan is a waza where shidachi and uchidachi meet and where no hostile intentions are announced until uchidachi grabs the tsuka to draw the sword when the two are within chika ma or have passed each other, when the attack is intended to cut down the opponent from behind.
Uchidachi:
taitō – nuki – osame – taitō
Shidachi:
taitō – nukiuchi – osame – taitō
Both uchidachi and shidachi start in taitō no kurai with their swords in the saya. Shidachi walks forward and meets uchidachi on the way. When they have passed issoku itto no ma, shidachi senses uchidachi grabbing the tsuka to draw the sword. He advances quickly with okuriashi and draws the short sword in steps with nukiuchi, i.e. pull and slash against the attacker's right hand or forearm. Shidachi advances with his left leg and applies pressure by pressing with his left hand against the back of the sword.
As uchidachi retreats to avoid being hit by a blow to the body, shidachi advances with okuriashi, maintaining pressure with the tip of the sword against his body.
Then both go back and insert their swords into the saya (osame) and finish in taitō no kurai.