My System Only Adds Security

The end of the world is coming, zombies are rampant, and alien beasts are raging. Others have awakened SSS-level combat abilities - fire control, thunder, and time stasis. And I awakened the [Security System]. The system doesn't teach me killing skills. It only allows me to [build walls], [hoard food], and [dig traps]. The rewards are all life-related skills: Strength +5, unlocking the formula [Cement], and obtaining the title [Junior Mason]. Everyone laughs at me for being a loser. Until the day when disaster truly strikes. They were chased by zombies and crawled all over the ground. They lacked food and clothing and waited for death in the ruins. And I was sitting behind the stone wall I built with my own hands, eating self-heating rice that I had stored for three months, and drinking pure water rewarded by the system. Beyond the walls is hell. Within the walls is paradise. Later, someone knelt outside my stone wall and asked me how I could become as safe as I am. I said: "The first step is to build a wall for yourself." "A hand planer will do, too." "That's how I came here."