Part of the reason why it became such a cultural phenomenon is the permissive license governing the use of the characters: https://touhou.fandom.com/wiki/Touho

Part of the reason why it became such a cultural phenomenon is the permissive license governing the use of the characters: https://touhou.fandom.com/wiki/Touhou_Wiki:Copyrights https://touhou.fandom.com/wiki/Touhou_Wiki:Copyrights