Short answers, pulled from the story.
Final Fantasy II was released on the 17th of December 1988 for the Famicom in Japan. The first international release of the original Famicom version came on the 28th of July 2021 as part of the Final Fantasy Pixel Remaster series.
The original Famicom release sold 800,000 copies. As of March 2003, all versions combined had shipped 1.28 million copies worldwide, with 1.08 million of those in Japan and 200,000 abroad.
Final Fantasy II uses a system where characters grow based on actions taken in battle rather than experience points. Characters who frequently use a weapon type grow stronger with it, and hit points and magic points increase through use. The system was designed by Akitoshi Kawazu and was later carried into the SaGa series.
Square's North American subsidiary cancelled the NES localization, titled Final Fantasy II: Dark Shadow Over Palakia, due to the aging of the original Japanese release, the arrival of the Super Nintendo, and the availability of Final Fantasy IV. The translator Kaoru Moriyama acknowledged the project was still far from complete when it was cancelled.
The Chocobo was designed by Koichi Ishii, based on a chicken he kept as a childhood pet. His original concept of a constant companion was rejected by Hironobu Sakaguchi, who instead incorporated the Chocobo as a rideable mount.
The character Cid and the Chocobo, both introduced in Final Fantasy II, became recurring elements in every main Final Fantasy game that followed. Firion and the Emperor were chosen as the representative hero and villain of Final Fantasy II in Dissidia Final Fantasy in 2009.