shut-in; stay-at-home; recluse
Jocular slang for a person who rarely leaves home, likening them to a security guard of their own house. Often used self-deprecatingly or humorously. Compare 引きこもり, which is more neutral/clinical.
See also: 引きこもり (ひきこもり)
On my days off, I end up becoming a shut-in.
He's a full-fledged recluse and hardly ever goes out.