Koyomimonogatari Episode 1: Koyomi Stone
Episode 1 of 12 of Koyomimonogatari, aired January 9, 2016, 25 minutes. Available with English subtitles and dub where released.
Episode summary
Before the events of Bakemonogatari, Koyomi and Tsubasa delve into the mystery surrounding a stone that was enshrined into one of the school's gardens.