Book Two: Spirits is the second season of the American animated television series The Legend of Korra created by Michael Dante DiMartino and Bryan Konietzko.

New characters introduced in this season include Unalaq and his children Desna and Eska; Kya and Bumi, the siblings of Korra's mentor Tenzin; Varrick, an eccentric and wealthy inventor and businessman from the Southern Water Tribe.

At the Southern Air Temple, Ikki disappears and Tenzin, Kya, and Bumi search for her while recalling their childhood with their late father, Avatar Aang.

In early 2011, during the production of Book One: Air – initially conceived as a standalone 12-episode miniseries – Nickelodeon decided to order fourteen additional episodes[13] to round out a standard 26-episode season.

[2] Joshua Hamilton and Tim Hedrick, writers for Avatar: The Last Airbender, contributed to the scripts of Book Two, and the season's episodes were directed by Colin Heck and Ian Graham.

Completed footage from Book Two was first made public in a June 2013 promotional video, in which Korra fights spirit creatures in an Arctic setting.

[20] The premiere episode was shown in full at The Legend of Korra panel at San Diego Comic-Con on 19 July 2013,[21] together with the release of a trailer video for Book Two.

[22] The premiere episode screened in advance at Comic-Con was positively reviewed by Max Nicholson of IGN, who appreciated the setup of the overarching conflict and the humorous writing.

[24] Writing for Vulture, Matt Patches highlighted the loose, handheld-style cinematography – challenging for an animated series – and the "weird, wonderful", wildly imagined spirits fought by Korra; "a Kaiju parade with beasts that mirror velociraptors".

[27] "The Sting", which premiered before "Beginnings", was equally praised by Nicholson for the improvement of the characterizations of Mako and Asami and their chemistry between each other, in addition to establishing Varrick as a "greedy mastermind" rather than as an eccentric businessman and entertainer as he had been before.

[30] Parts 1 and 2 of "Civil Wars" were equally acclaimed by Nicholson for the friendship between Bolin and Varrick, the sibling dynamic of Tenzin, Kya, and Bumi, a "strong, complex conflict" for Korra, the respective relationship of Tenzin, Kya, and Bumi, and Korra, Tonraq, and Senna as the heart of the story, and the twist behind Tonraq's banishment from the Northern Water Tribe and his imprisonment.

[33] For "Harmonic Convergence", Nicholson praised its spectacular action sequences, fleshing out more on Unalaq's intriguing evil purpose, the heroism of Bumi, and the animation.