The Touhou Project is a large series of shoot em' up games. Referred to as danmaku (or "bullet hell") games due to the emphasis on dodging tons of bullets usually in beautiful and complex patterns.
The games center around the shrine maiden Reimu Hakurei as she deals with many crazy incidents happening in the land of Gensokyo. Marisa Kirisame is also a main character that has been a playable character in nearly all of the games along with Reimu. She's a magician that has an affinity for stealing things and research in magic.
Each game in the series is about something going wrong and the main heroines going out to investigate and try and stop the culprit.
Touhou fans sometimes gets a lot of flack because of the series having an almost entirely female cast. As such, less informed people will often call it a game for pedophiles and creepy people, which is is NOT.
Here's some pictures of the craziness that can happen in these games.
