MSDOS
From OS-Tan Collections Wiki
A rarer character, MS-DOS is a cute but very shy little girl carrying around a keyboard and usually peeking around corners. The implication is that, like MS-DOS itself on non-NT versions of Windows, she is always lurking somewhere in the background, just out of sight.
She originally represented the DOS prompt and assumed to be a catch-all for all the DOS OSes but now more specifically represents MS-DOS.
See also: