Short answers, pulled from the story.
Final Fantasy IV: The After Years is an episodic role-playing game co-developed by Matrix Software and Square Enix, serving as the direct sequel to the 1991 title Final Fantasy IV. Set seventeen years after the original game, it follows both returning characters and their descendants as a new threat emerges tied to the return of the second moon.
The game was originally released in Japan in 2008 for mobile phones. It was ported to WiiWare in 2009, bundled into the PlayStation Portable compilation Final Fantasy IV: The Complete Collection in 2011, and a 3D remake launched on iOS and Android on the 24th of November 2013 before arriving on Steam for Windows on the 12th of May 2015.
The game was co-developed by Matrix Software and Square Enix, with Takashi Tokita serving as producer. Tokita had previously worked as scenario writer on the original Final Fantasy IV and proposed the sequel concept when Square Enix's mobile team approached him during development of the Nintendo DS remake.
Band abilities are a new type of combination attack introduced in The After Years, allowing two or more characters to coordinate their commands into a single powerful attack by spending MP from all involved party members. There are over seventy different Band combinations in the game, and the system is comparable to the Double and Triple Techs found in Chrono Trigger.
By August 2008, within the first five months of the Japanese mobile release, the game had reached one million downloads, not counting free downloads of the prologue chapter. By December 2010, paid downloads had exceeded four and a half million.
The WiiWare port received mixed reviews, holding an overall score of 69 out of 100 on Metacritic. IGN gave it 8 out of 10, while GameSpot scored it 5.5 out of 10. Despite mixed critical reception, Nintendo Power nominated it for both Game of the Year and WiiWare Game of the Year.