I remember reading the synopsis of a manga, where two people from different countries love each other, but the countries go to war. I think they were of royalty, one was a prince, and the other was a princess, but this might be a false detail. After the two countries go to war, one of them (maybe both) goes missing. The remaining one has to look for the missing lover with their friend.

The description is really hazy, but any name drop of a manga that has a country of light/day and country of darkness/night go to war would be very helpful.

Thanks for any help!