Reimu Main

"Basically, this is a term for a western Touhou player who refuses to pick Marisa or any other girl on the list, depending on the game. They are often hated by the western Touhou Project fanbase and are often seen as toxic. The large majority of Reimu mains are often aged 12 and below, but teens and adults qualify as this as well. And no, this term does not apply to Japanese players. To make matters worse, I'm a Reimu Main too."

- Susumu Takajima, in an interview in the New York Times

A Reimu Main is a derogatory term created by the western Touhou Project fanbase for players who often use Reimu Hakurei as their go-to character.

History
Reimu Hakurei's western reception was initially mixed, with the flaws being her voice and the way she fires her projectiles. When Touhou 6: The Embodiment of Scarlet Devil was released in the United States in 1992, a group of players in Denver, Colorado came up with the term after playing a few rounds, basically those who said that Reimu was their favorite character.

The term started spreading when it was covered in an issue of Nintendo Power, then to GamePro, then to GameInformer. Around three years after the game was released, the term was spread onto the internet.