One: Kagayaku Kisetsu e

Orihara Kouhei is a mysterious boy with a tragic past and tormented by memory loss in his childhood.

He had disappeared for a long time, then returns to fulfil the promises he made to several girls in his past which he had forgotten.

Note: The game was very popular and it was dominating that particular (romance-drama-ecchi) game genre in Japan that year.

It was so popular that there were several Drama CDs released, and finally the OVA about two years later.