Itsuki Mariko: Kyonyû shigoku (1989)

Mariko. The son of a wealthy family failed his university entrance exam and is currently retaking the exam. However, he doesn't go to cram school at all, and instead hangs out with his friends instead of studying. He has no money to spare, so his parents bought him a computer, and he is absorbed in online communication at night. He meets a girl named Rain through the online communication. The man becomes fascinated by her innocent and cute writing, and eventually he falls in love with the girl on the computer...