Mima is the only PC-98 character to appear on an official Windows cover, but not yet in a Windows game.
Although originally a very prominent character in the series (one of the earliest bosses/playable characters and appearing in almost every pre-Windows game from the very beginning), like many PC98 characters, she has entirely disappeared from the series from Embodiment of Scarlet Devil onward. She is occasionally depicted in fanart or doujinshi as having taken up residence at the Hakurei Shrine, along with Suika.
The bloody knife she carries in her original appearance may be a hint at her past, how she became a ghost, or why she became an "evil spirit."
It's unknown why she resents the Hakurei Shrine and if or how she may be connected with its past, but she seems knowledgeable about many things related to it, such as the Yin-Yang orbs only being properly usable by blood members of the Hakurei clan.