Yandere Kanojo is a gag manga series created by Shinobi published both online and in Monthly Gangan Joker. Both versions cover the same story and plot, but depict non-contradictory events not covered by the other version of the manga.
The "yandere" in the title is a combination of "yankee" and "deredere," and is not the same as the more commonly used yandere term.