Ninja Gaiden Sigma Plus

To perform the strongest Ultimate Technique, you must hold down until you see 2 flashes of different colors, you will see blue first, then red. When you see red, it's at the strongest technique. Release and you should kill your enemy instantly. If you're playing on harder difficulties then it might not kill them so be careful that some weapons will leave you vulnerable. The trophy will unlock after your 100th kill when using the strongest Ultimate Technique.