A mysterious girl from a far advanced race of humans comes from the future to Elijah's present, and insists that he help her on her journey. She is a scholar, set upon studying the lifestyle and history of Homo Sapiens, so that she will be able to understand why they went extinct in her own time, and maybe even bring them back.
Note, this story does not occur in chronological order. Some chapters are ahead, some behind, etc. I write the parts as I feel like it.

Cover is from https://www.pixiv.net/en/artworks/53790740