Harukanaru Toki no Naka de (遙かなる時空の中で Within the Expanse of a Distant Time?) is an otome (female romance) adventure game developed by Ruby Party and published by Koei. It is a part of Ruby Party's Neo-Romance label.
Because of Harukanaru Toki no Naka de's success, the game has give rise to a franchise including several sequels, numerous drama and music CDs, a manga series, two OAVs, a movie, and an anime TV series, and a live-action theatrical.
There are also spin-off (gaiden) video games starting with the third game in the series.
Source: Wikipedia, "Harukanaru Toki no Naka de", available under the CC-BY-SA License.