The Genius Mage Was Reincarnated Into A Swordsman Family - Chapter 1 -

Seong Eugene, a student at Gukcheon University, is recognized for his latent potential as a hunter but shows no signs of awakening by the age of 21.One day, his intense desire to awaken triggers his latent abilities, and he awakens with a new smartphone app.He invests five points to increase his physical attributes, specifically enlarging his penis to 16 cm. As he explores his abilities, he discovers he can conduct random draws for items and skills, acquiring several items and a complete recovery skill. His unique ability allows him to enter fictional worlds, and he decides to test this by entering an AV film he watched a week earlier, SV-7495.

Anyone who could construct a stable Spell Model could become a Wizard — that was the Wizards’ ultimate secret! Having been given a new life as the son of an aristocrat and armed with a super quantum computer from his past life, Spell Models came as easily as breathing to Merlin. With this overwhelmingly huge advantage, would Merlin become the greatest Grand Wizard of all time?

- Description from Novelupdates

This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.

Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.

“Please save us, Savior Dono!”

Kuroki nodded, deciding to save the demon king due to an unexpected turn of event.

The most feared Assassin in the world died because of vengeance.