All five fingers are bent like you have a clenched something. You should not have space left in the palm. Clench hard as if you are squeezing a stress ball and tighten the thumb. The arm and the back of the hand have to be parallel and when you look from the side, the back of the hand and the fist have to be at a right angle.

This is the same as the Seiken but you use the third joint of the forefinger and the middle finger.

These are the middle muscles between the little finger and the wrist when you make Seiken and set the fist vertically. Use this part the same way you use a hammer, the fist and the wrist have to be together and fixed.