Memai wa Madoi no Tsugai

On the day of the earthquake, Hato—an Omega unable to return home—finds shelter for the night in a secondhand bookstore run by a man named Kazumi.
"In times like these, I guess you could say we're in the same boat."
Touched by Kazumi’s quiet kindness, Hato begins to feel a faint affection for him.

A few days later, Hato happens to visit a bar where Kazumi works part-time. But as an Alpha, Kazumi instantly senses that Hato is not only an Omega—but also someone deeply compatible with him...!?

(Source: Shinshokan, translated)

Note: Includes one extra chapter.