Dekkkkarian

Gakuto Watari is a highly educated elite, but his extreme arrogance about his academic background has led to his total defeat in the job hunting wars, turning him into a toxic NEET who does nothing but lurk on internet message boards.

Suddenly, he is abducted by giant aliens known as a "Dekkkkarians." Under the guise of "rehabilitation," he is forced into manual labor in a mysterious underground facility alongside other middle-aged men mooching off their parents.

Naturally, his high-spec pride refuses to tolerate such tyranny and oppression. With a brain packed with extensive knowledge, he prepares to shut them down with logic and debate—or at least he would, if he weren't too terrified and overwhelmed to muster the courage...

(Source: Kadokawa, translated)