Can you recommend a novel where the male protagonist meets a future person who traveled through time and space?

Seeking the name of the novel!
In a novel, the male protagonist met a future person who traveled through time and space to the male protagonist's era one day. After meeting the male protagonist, he was very excited and said that the male protagonist had invented many things. He was the greatest scientist in the future. He even asked the male protagonist for an autograph. Later, the male protagonist's mind seemed to have a machine collection with all kinds of things. Later, someone asked the male protagonist to help him design high-end weapons. Two of the male protagonist's girlfriends were lesbians.

Answer 1

"Letter from the End of the World", the male protagonist Yuan An received a text message from the future and began an adventure about courage. He traveled through time and space, challenged disasters, and was blocked by the brave. It matches the plot you provided. I hope you like this fairy's recommendation. Muah ~😗