Apocalypse Zero, known in Japan as Encouragement of Resolve (覚悟のススメ, Kakugo no Susume), is a manga series written and illustrated by Takayuki Yamaguchi. It was serialized in Akita Shoten's Weekly Shōnen Champion from July 1994 to August 1996.

The manga was adapted into a two episode original video animation in 1996, animated by Ashi Productions and produced by Big West [ja], Victor Entertainment and Tomy.

Kakugo and Harara are brothers trained by their father, Oboro, to slay monsters that have begun roaming the streets of a post-apocalyptic, 21st century Tokyo following a devastatingly, powerful earthquake. To aid them in their quest, Oboro entrusts his two sons with Fortified Armor Shells (強化外骨格, Kyōkagaikokkaku), cyborg exoskeletons forged using the souls of deceased warriors by their grandfather, a former scientist of the Imperial Japanese Army during World War II, Shiro Hagakure. However, Harara becomes possessed by a mysterious evil from deep within his armor, mutating his body as well as filling him with a desire to destroy all of mankind to help cleanse the Earth of contamination. Some years later, Kakugo moves to "Reverse Cross High School", located in one of the ruined districts of Tokyo near the castle from which Harara commands their demon army. It is now up to Kakugo to defeat his evil sibling and put a stop to their wicked legions.

The Apocalypse Zero manga series was written and illustrated by Takayuki Yamaguchi. It was originally serialized in the Akita Shoten magazine Weekly Shōnen Champion from 1994 to 1996. A total of 11 tankōbon (chapter collections) volumes were published by Akita Shoten. An English translation of the manga was published as a graphic novel in the US by Media Blasters beginning on January 19, 2005. The manga was sold shrink wrapped, presumably due to the large amount of violence. Only six of the original 11 volumes were translated and released, as Media Blasters chose to cease publication of the series in early 2007.

The manga was published in Italy by Dynamic Italia, flipping it in a left-to-right format.

From 2010 to 2014, Yamaguchi wrote Exoskull Zero, a reboot of Apocalypse Zero featuring a similar protagonist in a slightly different plot. It was published in Akita Shoten's Champion Red magazine.

From 2015 to 2021, Yamaguchi wrote Efu no Shichinin ("The Seven of Efu"), a prequel of Exoskull Zero.

The Apocalypse Zero anime OVA was co-produced by Victor Entertainment, Tomy and Big West [ja], it was animated by Ashi Productions and directed by Toshiki Hirano. It was released in Japan in two volumes from October 23, 1996, to December 18, 1996, on VHS and Laserdisc. The OVA was planned to have ten episodes, but was canceled after the completion of the second episode. The reasons for the OVA's cancellation are currently unknown. The anime was released in Italy in 1999 on VHS, licensed by Dynamic Italia. The US license for Apocalypse Zero was acquired by Media Blasters who created a dubbed English language version of the anime translated by Takashi Sakudo and produced by Bang Zoom! Studios. The two VHS volumes were released from June 20 to August 22, 2000. A DVD release containing both episodes was released on August 28, 2001.