Yes, Sensei

Yes, Sensei is a Multiplayer Achievement in Halo: Reach. The achievement is awarded if a player earns a First Strike medal in a Matchmaking game.

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