Gameplay-wise, the main series games are vertical scrolling shooters divided into 6 stages, with a bonus Extra stage unlocked after beating the main game without continues. Despite the dark insinuations of some characters' backstories and origins, and the stakes of some incidents, battles in-universe are more akin to fair-sportsmanship duels that prioritize beauty over efficiency, and the villains of most games run on White-and-Grey Morality. After beating up several tangentially-involved bystanders in the early stages of each game, they eventually discover the person or parties responsible for the incident and trounce them and their friends or Battle Butlers when all's said and done, many of them show up uninvited to drink tea or attend afterparties with the protagonists, and quite a few go on to become friends, acquaintances, or even playable allies in future games. In any case, the duty of resolving said incidents falls onto the shoulders of main protagonist and Miko Reimu Hakurei, her best friend Marisa Kirisame, and typically one or two other recurring characters per installment. Most main games in the series revolve around an "incident" that occurs, ranging from harmless curiosities like flying ships, to concerning events such as land-smothering mists, to threats to Gensokyo itself like otherworldly invasions. Although much of Gensokyo reflects an antiquated Japanese society, most games in the series take place in the real-life year of their release, with a steady continuity and the gradual introduction of more Outside World technology and concepts as the years go on.
Created in response to the waning belief in such entities by modern humans and the advancement of technology, Gensokyo was (mostly) isolated from the outside world by a boundary of fantasy and common sense in the 1800s, creating a region where humans and youkai live in delicate balance to maintain co-existence. The basic story of the setting is set in the land of Gensokyo, a Fantastic Nature Reserve hidden in the mountains of Japan, and the various humans, youkai, gods, and other mythological creatures living there.