Kazuki Instant Blade - Mist

In the tenth episode, as Kazuki tries to take the Vassal Katana from Raphtalia, who was restored to her older form by the weapon, she easily defeats him by immobilizing him with the move "Instant Blade - Mist", which will decapitate him if he takes a step. In the proceeding episode, as Kyo berates Kazuki for failing to have Raphtalia stay imprisoned and acquiring the Katana Vassl Weapon, which Kyo was aware of Kazuki's plan to use it to kill him, Kazuki ignores his underlings and moves before they could diffuse Raphtalia's time-delayed death attack and winds up getting decapitated from the shoulder up.

Example of:
Too Dumb to Live