Since I don't have direct access to an officially published work with this exact title (it may be a niche doujinshi, a fan translation, or an upcoming series), I will draft a based on the archetypes and keywords you provided. You can adapt this to the specific plot you have in mind.
Coming [Month/Year] "Age is not a number. It's a weapon." Arimura Nozomi- Wakui Mito - The Virile Old Man...
Their savior? A grizzled, 78-year-old retired construction foreman with thick wrists, a booming laugh, and a presence that fills a room. They call him the Oni no Jiji (Demon Gramps). Since I don't have direct access to an
Arimura Nozomi lives by the book. As a junior analyst in a Tokyo security firm, she believes data, rules, and procedure are the only paths to success. Wakui Mito, a cynical street-smart courier, believes the opposite: rules are cages, and only the ruthless survive. They have nothing in common—until a botched corporate heist traps them both in an abandoned subway tunnel. It's a weapon
When two very different young women—the earnest Arimura Nozomi and the enigmatic Wakui Mito—cross paths with a brash, unfiltered, yet inexplicably powerful elderly man, their definitions of strength, masculinity, and honor are shattered and rebuilt.
Dismissed as a relic, the old man does something neither woman expects: he rips a steel door off its hinges with his bare hands, hums an old Showa-era enka tune, and walks them out past a dozen armed men without breaking a sweat.
Arimura Nozomi, data-driven and fragile. Wakui Mito, street-smart and broken. When a city-wide blackout traps them with a ruthless gang, their only ally is a 78-year-old man with calloused hands and a terrifying calm.