Based on the original visual novel series.

Shirogane Takeru is a typical high school student with a lazy attitude and a love for the virtual reality mecha battle game Valgern-on. Even though he didn't really wanted it, he is popular in school mainly due to his daily fights with his osananajimi (Sumika) attracting too much attention. His life takes an unexpected turn when he finds a girl (Meiya) he doesn't remember ever meeting in his bed one morning. Whom later revealed to be the heiress of one of the biggest zaibatsu. She immediately moves to his house and starts changing his life for the good with her one-track-mind and unlimited resources...

(Source: VNDB)