Milliela is a 2D fictionnal character both Okumura and Lilysa love. Her and Lilliel are from the same show.

2.5 Dimensional Seduction
"I have no interest in real women! My wife, Lilliel, is a 2D girl!" But something unexpected appears in front of Okumura, the president of the Manga Research Club... A real Lilliel? An exciting cosplay love comedy begins!!