Retsu!!! Date Senpai (烈!!!伊達先パイ) is a manga series by Shinsuke Kondō that run in Weekly Shōnen Jump.
Katakura is a high-schooler who loves Mego, a girl that unexpectedly loves him also. Lovely couple, huh? The problem is "Date-senpai", Mego's brother that is a Sengoku era maniac. He talk in a very polite way and even brands a sword and rides a horse (at school!). What will this love and gag story turn into?