Mii and Kei are characters from Shin Megami Tensei IV: Apocalypse.
Shin Megami Tensei IV Apocalypse
Two crude elderly twin Gaeans that follow the teachings of Yuriko. They succeeded her as the Ring of Gaea's leader to serve Lucifer after her death, later being forced to lead the weak Yuriko faction after Maitreya and his faction effortlessly defeat them. The two seek vengeance against Flynn and Maitreya as a result.
The two are vulgar deviant women, cursing when insulted and talking about having sex with the young men before them. The two raised Toki from birth, treating her as an expendable tool who must repress her emotions to live and serve. They promise to lead Nanashi's group into Tsukiji Konganji in exchange for taking Toki, making it clear that her job is to kill Flynn and Maitreya in the promise, before lying and saying they'll compromise on Flynn's death.
- The two are gender inverted versions of the Dark Priest Gaeans, including floating above the ground.
- Their names are a reference to the popular late 70s early 80s pop duo Pink Lady, members Mitsuyo Nemoto (Mii) & Keiko Masuda (Kei)