I Built an Old Refuge

The protagonist is in a terrifying world where spiritual energy is revived (actually the awakening of ancient gods), and he inherits a dilapidated castle (sanctuary) at the beginning. He couldn't just go out and kill monsters, because any tentacle outside could kill him. He must hide behind the scenes and drive the survivors and "cleaners" outside to collect resources for him by upgrading the shelter, formulating rules, and launching tasks.