Pretty young girls have been captured and are being sold off at an illegal auction. Marquess Collide is engaging in human trafficking, and all her buyers are evil nobles as well. By royal order, Lugh the assassin, Dia the mage, his assistant Tarte, and Maha the intelligence expert begin their investigation of Marquess Collide. However, Dia is captured by Marquess Collide and put up for auction--

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--

Officially a family of renowned doctors and assassins behind the scenes, the house of Tuatha Dé is the right hand of the kingdom. Trusted to become his father's heir, Lugh assists his father with his mission. However, there are those who are displeased by Lugh's success. Lugh defends his status in a challenge against them--

A group of girls were toughing it out despite their impoverished circumstances. Though they had nowhere to live, they ran a business and enjoyed their lives together. However, an orphanage captures the girls and forces them to move into the facility. Motivated by subsidies, the orphanage puts the girls to work and even has them work as ladies of the night--

Lugh heads to the neighboring kingdom of Swoigel. Once a month, he travels to the Viekone region in order to visit Dia. During his visit, together Lugh and Dia develop new spells. Meanwhile, left back home by themselves, Tarte and Maha hold a tea party together. While Lugh is gone, they have a fun time preparing a special meal together, but--

With the success of his cosmetics brand Orna, by acquiring financial power and the Balor Trading Company's information network, Lugh has gained even greater strength as an assassin. However, since being reincarnated in this world, Lugh still has not completed a proper assassination. Then, Lugh's father Cian tells him that he doesn't have to become an assassin--

Lugh accepts an assassination job and heads to the merchant town of Pisear with Tarte in order to determine if his target is worth assassinating. While there, Lugh witnesses the tragic sight of people suffering because of his target. Based on information gathered by Maha, Lugh plans his assassination.

While Lugh is practicing his magic on an uninhabited island with Tarte, Maha shows up with some information. Civil war has broken out in the Swoigel Kingdom. Concerned, Lugh visits Dia, but the region of Viekone is peaceful. Dia is indifferent to Lugh's concerns and suggests they go on a date.

Lugh is hired to assassinate Dia by her father Count Viekone, who is an old friend of Lugh's father Cian. Cian asks Lugh to fulfill Count Viekone's request, saying he'll carry out the assassination instead if Lugh turns down the job.

The Goddess has been summoning and reincarnating a broad range of people in order to stop the Hero from destroying the world, but they all seem to have ended in failure. However, all the reincarnations that had been conducted until now were for the purpose of gathering data. With the data she has gathered, she summons the person most likely to stop the Hero.