These Two Will Be Married In 100 Days

A Twitter comic by Yuuki Kikuchi about a croc living his last 100 days.

Later collated by Shogakukan for print release.

First comes marriage, then comes an earthbound love that is out of this world! From the day his parents named him, Nasa Yuzaki has been destined for outer space…or so he believes. But while trying to join the space program, he is thrown for a loop when an accident introduces him to Tsukasa, a mysterious girl with strange powers. Is she an alien, a moon goddess or something else? Since she insists on marrying him, Nasa has plenty of chances to find out!

(Source: VIZ Media)

Notes: The 16th volume includes the 4 chapter prequel "FLY ME TO THE MOON".