I See One Second Into The Future: Loner In The Apocalypse - Chapter 16 A Story?

Payload specialist, Tang Yue, who is a mechanical and electrical engineer by training, is left stranded on Mars when he receives news from his AI robot assistant, Old Cat, that Earth has exploded. He believes himself to be the last human in the Universe.

With a marriage contract forcefully done, he married her, and all she could do was comply, and resent him deeply for that and for all the following misunderstandings they faced.
However, it was already too late when she understood she actually loved him.

He Lang died by his own hands for the sake of his imperial younger brother’s ambition, whom he loved. He was offered to be reborn in exchange for giving up his past romantic feelings. Reborn without the burden of his romantic feelings, he brings with him a manual to new worlds. He wholeheartedly followed the instructions of the manual to complete the tasks, not knowing that the originally slag gong was blackening…
He pleaded to his affectionate Emperor brother to release him, he pleaded to the paranoid prisoner next door, but until the end he remained baffled.
In the end, he discovered that the full name of the manual was – “Slag Shou Cultivating Manual”
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- Description from Novelupdates

The young lord of a small and weak country saves a dragon beside the sea one day.