Hangetsu (Half Moon), formally known as Seishan, is one of the less popular kata amongst the younger student of Shotokan. Many very senior karateka have commented however that they gained an appreciation for the kata with age and experience.
The one characteristic of this kata that makes it so important in the Shotokan syllabus is the attention to the breathing. Different associations use breathing in this kata differently, but all place emphasis on the deep inhalation and exhalation, particularly on the opening sequences of uchi-uke -gyaku tsuki.
When applicated, the techniques for this kata are perfect for close-quarter defence and close-quarter counter-attacks, with the feet movements representing the desire to fight from a close-proximity, with the intent of pressurising, unbalancing and thus weakening the opponent.
Other styles practice their own version of Hangetsu, and many do not consider this kata as a representative kata of the Shotokan Style. Many view Shotokan as a style characterised by the long deep stances for stability and power. This kata mostly uses hangetsu-dachi and also uses neko ashi-dachi, which although powerful and rooted are not quite as long and low in the hips. However, such opinions do not negate the value of practicing Hangetsu.