Edit: it's complete, so I've compiled in a volume as posted here: https://nyaa.si/view/1250658.
You can read it for free on MangaPlus.
But if you would like to download it to have it offline...
The eternal darkness which people call “night”. Long long ago, there was an opposite to this “night”. Something far brighter than the light of their lamps, the light of hope for humanity. Seek out the forgotten “morning”.