Crystal Guardians

All of the releases in the Crystal Defenders series are tower defense games composed of multiple stages, each consisting of a top-down view of a winding path. Stages contain 31 waves (or levels) of enemies that enter the area on the left side of the screen and walk along the pathway towards the goal, a set of crystals off the right side of the screen. The goal of the game is to protect the crystals from enemies by strategically placing troops of various "jobs", or classes, alongside the pathway to defeat the enemies and prevent them from reaching the other side of the map. Troops can attack within a circular area around them, moving to do so if required such as for sword-using fighters.

Different classes attack in different ways, with some classes having effects such as causing damage over time or slowing enemies. Each enemy that reaches the crystals takes one; the game ends if twenty enemies reach the crystals during a stage. Players can also summon Espers at the cost of some crystals to either cause damage or have effects on all enemies on screen.

Three developers have worked on the Crystal Defenders series; the series as a whole was supervised by Final Fantasy franchise owner Square Enix. External studios Mobile Software Foundation and Winds worked with Square Enix on Crystal Guardians and Crystal Defenders, while Square Enix worked alone on Crystal Defenders: Vanguard Storm. The Crystal Defenders series uses the recurring setting of Ivalice, specifically recycling character designs and aesthetic elements from the Nintendo DS title Final Fantasy Tactics A2: Grimoire of the Rift. Despite having a different genre from previous Tactics titles, the team aimed to keep the game as faithful as possible to the world and aesthetic of Ivalice.

The series reuses music from Tactics A2 composed by Hitoshi Sakimoto and other composers from Sakimoto's studio Basiscape. The character designs were created by Ryoma Itō, who had previously worked on Final Fantasy Tactics Advance, Tactics A2 and Final Fantasy XII: Revenant Wings. The series was produced by Takehiro Ando of Square Enix's mobile division. Crystal Defenders was Square Enix's first game for smartphones.

The series, especially Crystal Defenders, has sold well, with Defenders achieving one million downloads worldwide as of December 2012. Overall critical response to the series has been mixed, however, with Defenders receiving poor reviews and Vanguard Storm earning a more mixed reception. Reaction to the presentation of the mobile versions of Crystal Defenders and its ports were mixed; Connor Egan of Slide to Play noted that it "faithfully reproduces the look of the Final Fantasy Tactics series", but found that the control scheme made the gameplay area feel small and cramped. Sam Bishop of IGN criticized the visuals of the PlayStation 3 port of the game for being "minimally animated" phone graphics with a border around them, though he praised the music.

IGN's Ryan Geddes, in reviewing the Xbox 360 version, was much harsher: he dismissed the character designs as "generic looking" and the animation quality as "dull", though he had no complaints about the music or sound effects. Tom McShea of GameSpot had similar complaints about the Xbox 360 version, calling the character graphics "devoid of personality" with minimal animation. The gameplay received similar reviews: McShea criticized the game's artificial intelligence and termed the gameplay "lifeless and uninspired", and Geddes concluded that the "gameplay is stale and the concept is poorly executed". Both Egan and Bishop were more positive to the game, feeling that it was a competent example of a tower defense game, but Egan felt that the "ungainly and amateurish controls damage the experience", and both reviewers found the game to be very difficult to complete.