Reimu Hakurei is a "shrine maiden", a young girl whose job was to protect shrines of the Shinto religion in feudal Japan. The fabric of reality is torn when demons from the parallel realm known as "Illusion Village" invade the human world through the shrine Reimu is guarding. The young girl must defeat the demons and seal the entrance from the other world.
The first of the Tōhō series is similar to Breakout-style games, since it is composed of one-screen levels, with the typical goal of destroying all the bricks (cards, in the case of this game) by manipulating a ball. However, unlike in most Breakout clones, the player controls a real character (Reimu) instead of a traditional paddle. The specific gameplay mechanics are also a bit different: the ball cannot fall "below the ground"; if it hits Reimu, she loses a life; the player has to press a corresponding key to hit the ball in close range.
The game can also be considered a shooter, since Reimu can (and often has to) shoot the ball when it is high in the air, to change its trajectory and destroy cards. Also, after every five "regular" levels there is a "boss level", which plays similarly to top-down shooters, and during which Reimu also has to defend herself from projectiles shot by the boss, either dodging or shooting them.