Hatsukoi Monogatari

An ordinary Japanese student finds a floppy disk on the street; using his computer to load data from it, he miraculously summons Foltjunia, an intergalactic warrior who fights evil in her robotic armor with three companions. However, Foltjunia has lost her powers and as a result stays with the hero, giving him advice as to how to conquer the love of a schoolmate.

[from MobyGames]

Your father gets a job transfer and is taking the family with him. You have three months to make your feelings known to your crush.

The initial character creation determines whether this happens in primary, middle, or high school.