The world's finest Assassin accepts the Goddess' request to assassinate the Hero. After defeating the Demon Lord and saving the world, the Hero will then use his power to destroy the world. The Goddess wants the Assassin to be reincarnated in another world and assassinate the Hero in order to save it. After being betrayed and killed by his client in his previous life, the Assassin accepts her offer in order to relive his life in a new world, but--

Lugh's magic teacher is a pretty girl named Dia. Being a few years older than Lugh, Dia treats him like a younger brother and sneaks into his bed every night in order to sleep next to him. Because he needs her to teach him magic, Lugh can't complain, but gradually he and Dia grow closer--

The goddess is formulating a plan to stop the Hero's rampage. After defeating the Demon Lord and saving the world, next he will use his power to destroy the world. The goddess has decided to summon the souls of professionals from other worlds and reincarnate them. She summons the soul of the world's finest special forces soldier who excels in combat and asks him to defeat the Hero, but--