2K-tan, also known as Nijikay Tan (虹界 タン), is a personification of the Windows 2000 operating system in the OS-tan series—an unofficial Japanese meme where computer operating systems are depicted as anime girls. She is portrayed as a responsible and mature older sister figure, often helping and guiding the younger OS-tans. She is usually depicted as reliable, diligent, and somewhat strict, embodying the stability and dependability associated with Windows 2000.