Read Magika no Kenshi to Shoukan Maou Manga:
15 years ago the world discovered magic as well as mythical beings (basically beings from various legends) in another dimension. Humankind learned to summon these dangerous mythical beings and use their power to great effect. Seven countries formed contracts with these "gods" and gained their allegiance as a result. Gods will chose their summoners on their 14th birthday and give them a stigm more.. a. Schools have been set up to train summoners and magical swordsman (basically bodyguards that give the summoners time to cast their spell) as a result. 15 years later after the finding of magic Kazuki Hayashizaki is chosen as a summoner and given a stigma to indicate that.