Tettsui Oroshi Ganmen Uchi is a technique in Kyokushin karate. It translates to 'Hammer Fist Descending Strike to the Face.' This technique involves delivering a powerful downward strike with the hammer fist to the opponent's face. The term 'Tettsui' refers to the hammer fist, 'Oroshi' means descending, and 'Ganmen Uchi' indicates a strike to the face. It is a devastating technique commonly used to incapacitate or stun the opponent.