Upon waking up, Souichi has somehow become a Demon King. In preparation for the war between Demon Kings, he must strengthen the defense of his own dungeon. However, the skill Souichi was given meant that he could only summon monsters of the weakest rank. Souichi is in despair knowing he can’t win with this war… But in reality, the skill he was given has great potential. With “gacha” and “combination” and making full use of the summoned monsters he aims to become the strongest Demon King !