Nobunaga no Shinobi: Nobunaga to Minarai Shinobi
English name: Ninja Girl & Samurai Master: Episode 0
Genres: Comedy
Type: Special, Episodes: 1
Aired: Mar 25, 2016
Studio: TMS Entertainment
Source: 4-koma manga
Rating: PG-13 - Teens 13 or older
Synopsis:
Oda Nobunaga saves a girl from drowning one day. She clumsily tells him that she's a shinobi. Instead of attempting to kill him, she swears to serve him one day after hearing his plans to unify Japan.

(Source: Crunchyroll)