Year 2018.

The world experimented with a great change. A large tower appeared in 7 different countries exuding strong strange energy that the devices couldn't identify. After their appearance, during seven days, people around the world began to experience changes in their bodies, some became faster, some stronger and even some people began to manipulate the strange energy that sometime after was being called as 'mana', the energy with the capacity to make magic. However, the principal change that everyone experiment with was the appearance of the System, similar to the ones found in RPG games, where one could see their level, stats, skills, and equipment.

Some people were already some levels up, but the majority were on levels down Level 10. Also, kids under the age of 12 didn't get the System. But during that week, a twelve-year kid was having his thirteen birthday, and during the party, the System appeared in front of him and he told his parents. After that, different cases happened around the world saying that the kids who were celebrating their thirteen-year-old birthday were having the System appearing. With that, the governments agreed that the System would become active after the person becomes thirteen years old.

After the seven days passed, and all of those changes happened, the towers disappeared just like they appear, but portals occupied their places and monsters began to crawl out from them, making the people panic. More than twelve portals appeared in all the world, and the swarm of monsters seemed to have no end. A war began, and during one year the monsters had the upper hand until one day ten people appear with powerful skills and levels. The strongest between the ten was a man in his twenties that was on Level 20. He found, like the other nine, that killing monsters gave him experience points which help him level up, and on each level up he would be given 1 stat point, and after leveling up 5 levels, all his stats will increase in 1 point. After that information was disclosed to the public, humanity began to win the fights and also began to close the portals after killing the boss inside.

Nonetheless, portals continue to appear all around the world. Some portals were of higher level, and the people couldn't fight there. The good thing about those portals was that they appeared on islands, where the monster couldn't go to other places and wreak havoc.

Just like that, the world entered a new era, the portals were called 'dungeons' and a dungeon hunter became an occupation recognized by the authorities.

Each country created its Hunter's organization to control the interventions of the dungeons. Also, crafters and artisans make their debut, showing their ability to work with the corpses and materials which hunters recollected on their interventions, and in that way, the occupation 'Dungeon Hunter' became one of the best pay jobs, but also, the danger was more, the simple reason was that one could be get killed during a raid.

The Dungeons were classified into 7 ranks and the governments also give the minimum level which one need to at least survive, F (minimum level: 10), E (minimum level: 20), D (minimum level: 35), C (minimum level: 55), B (minimum level: 70), A (minimum level: 100), S (minimum level: 120). That's the official rank, but there was a case where a monster was an SS-rank that was only possible to kill because his weakness was the water, and was pushed to the ocean where it died. For the time being, dungeons ranked from C and up, were places completely out of human range.

With that, not everyone decided to become a dungeon hunter, but instead, continue to live normal lives. Of course, the kids were anxious to become dungeon hunters that were seen as heroes of humanity.

Another year passed, and the System seemed to have an update. Now people could take missions to get a class: warrior, guardian, archer, fire magician, water magician, light magician, swordsman, etc. However, those 'class missions' were very strict, and also the difficulty was on the same level as a D rank Dungeon.

After two years, the first C-rank Dungeon was cleared, giving more hope to people.

But after the update of the classes, leveling up began to be more difficult. The dungeon hunters that were on the highest levels (60+) began to experiment with problems to level up. Finally, after three more years, in 2024, the first dungeon hunter became halted on level 70 and couldn't level up more.

Then, in the year 2027, the first B-rank Dungeon was cleared. The raid consisted of 50 hunters on levels between 65 and 70, and the casualties were 10 hunters of Level 65, 10 of Level 66, 4 of Level 67, 1 of Level 68, 5 of Level 69, and 5 hunters of level 70, leaving just 15 hunters alive, 1 Level 66, 6 Level 68, 5 Level 69 and 3 Level 70. It was a big loss for humanity.

Using that raid, the world calculated that they need at least 100 hunters of Level 70 to clear an A-rank dungeon, and more than 300 of the same level to clear an S-rank dungeon.

8 years after, on April 15th 2035, Sora Reith activated the System on his tenth birthday.

Sora began to be an orphan two years after he was born, when his dad died on the B rank dungeon raid. His dad was a hunter of Level 68 when he died. He was one of the strongest hunters on their country: The United States. Sora's mother died after giving him birth.

All the inheritance left by his two parents, was taken and saved on the Hunters' bank, and they would return and gave to him until he turns 15 years old. That was the arrangement they give to the orphans principally because they would have already awaken the System, and after two years of training, they could become hunters and pay the care of the orphanage.

Yes, that's right. The orphanage where the young Reith was living at, was one of the lot of orphanages which the Hunters Organization operate firstly to get more hunters and secondly, to take care of the kids of hunters that died during missions.