I Have a Mystery Store

This is a world that has been conquered and occupied by alien races. The human race has become the blood food of all major alien races. The human race can only survive in underground shelters. The protagonist travels to this world, obtains the qualification to be summoned by the mysterious store, and has the means to protect himself. The powerful alien race, the weak human race, the bunker lord who defends the human race to the death, and the partners he met along the way. The meaning of the word "guard" gradually becomes clear in the protagonist's heart.