Mirai Shounen Sharaku

Azuma Shuu, 26 years old and never had a girlfriend, is suddenly pushed down in the storeroom of the supermarket where he works by a beautiful young man he’s never seen before, who pleads, “Please bear my child.” The young man, who hit his head, introduces himself as Yamamoto Sharaku and claims to have come from the future, though most of his memories are missing. Thinking he’s a complete nutcase, Azuma still ends up taking him home...!?

(Source: Julian Publishing, translated)

Note: Includes one extra chapter.