Yes, Sensei

Yes, Sensei is a Multiplayer achievement in Halo: Reach. It was awarded when a player earned a First Strike in a matchmaking game.

Following the shutdown of Xbox 360 Halo online services on January 13, 2022, this achievement is no longer attainable.

Trivia
The achievement's name is a reference to the 1984 film The Karate Kid, in which the antagonistic Cobra Kai dojo advocates striking first, and striking without mercy. Sensei means both "teacher" and "first strike" in Japanese.