たたかえ！プリンセス

Hero is a boy who likes inventing just as his genius parents who live abroad. One day a mysterious capsule with a girl inside it falls from the sky. She is a princess of some star in the Universe. In her royal family there's a habit of practice as a servant on other stars, but she failed the first attempt and came to train to the Earth where invasion level was low. Still doubtful, hero allows her to stay with him in the mansion and he's got no complaints with her cooking and cleaning. She even starts to visit the same school as his cousin. Then one day a shady figure shows up at the mansion...

[From vndbreview]