The story begins with Yamada Giichi, a 42-year-old, single, and content local government employee, who tragically dies in a terrorist attack. He finds himself in a traditional Japanese room, confronted by a casual, self-serving blond, blue-eyed God. Giichi learns he is one of 136 victims chosen for "Isekai Tensei" (reincarnation into another world) as entertainment for the deities. The new world, Milnerze, is a flat, medieval-tech realm with magic, powerful monsters (Orcs), and a bureaucratic knight order supplemented by Adventurer's Guilds. Giichi, pragmatic and observant, negotiates with God, who offers one special ability. Giichi chooses "Summoning Magic," which allows him to summon one personal possession for 12 hours a day. He registers his 1LDK apartment, which miraculously retains its electricity, gas, and water, and resets all its contents to the moment of his death, providing infinite food and supplies. He is reincarnated in the vast, dangerous "Oak Forest," where the nearest town is an Orc settlement.
Giichi soon encounters Ninomiya Nene, a new preschool teacher, and four six-year-old children (Ren, Sora, Yua, Sakura), all fellow reincarnators. Nene, timid but fiercely protective, possesses a "Translation" talent, while the children have various attribute magics (Light, Wind, Fire) and Spirit Magic (Sakura). They have already faced immense hardship, including an assault by two other male reincarnators (Toshimitsu and Shigeru) and a subsequent attack by Orcs, during which Nene was injured. Giichi, using fireworks and his calm demeanor, rescues them and invites them into his summoned apartment, offering them their first proper meal, bath, and safe rest, rekindling their hope.
Inside the apartment, Giichi forms a "party" with Nene and the children, allowing them to share information and experience points. They discover a "bug" in the system: by shouting spell names towards the void outside the apartment's balcony, they can increase their magic proficiency without consuming magic or casting actual spells in Milnerze. This allows the children to rapidly level up their magic abilities (Ren, Sora, Yua to Level 5, Sakura to Level 8). The whimsical God, monitoring their progress, appears in a rage to "patch" the system, but Giichi cleverly uses Sakura's tears and vulnerability to argue for their need for strength, causing God to reluctantly allow their current power-ups to stand.
Meanwhile, the two male reincarnators, Toshimitsu and Shigeru, are captured by Orcs and forced into a gladiatorial fight. Toshimitsu is quickly killed. Shigeru attempts to summon a water spirit (Undine) during a rainstorm but fails to form a contract, leading the displeased spirit to kill him. God observes these events, noting the Orcs are now tracking Giichi's group with trained "Red-Eyed Wolves" for revenge.
Unaware of the immediate danger, Giichi decides to test Sakura's Spirit Magic. He carefully summons a water spirit, which Sakura affectionately names "Munch." Sakura, with her pure heart, easily forms a contract with Munch, who, due to another system "bug" related to the apartment's unique properties, becomes a persistent ally even after the apartment disappears. Munch's duration is limited, but it can assist in foraging and, as discovered later, combat. During an outing, Nene injures her ankle, and Munch provides a comforting massage. Sensing an approaching threat, Munch flies off, leading to Ren and Yua's existence levels increasing. Giichi investigates and finds a dead Orc, killed by Munch, providing the group with their first meat for a meal.
From a group of desperate, vulnerable survivors, the party has gained a secure base, significantly enhanced their magical capabilities, acquired a persistent spirit ally, and found a resourceful leader in Giichi. They are now better equipped for survival, though unknowingly targeted by vengeful Orcs.
