"Kouryakubon" wo Kushi Suru Saikyou no Mahoutsukai

The Hero had always derided Magnus as a worthless wizard, and eventually, he could take no more. He left the party and ventured forth, coming across a vendor who sold him a sacred tome penned in the language of the divine. The book defied his expectations, containing a far-reaching compendium with precise intel about defeating the Demon Lord. Magnus used the knowledge from the book to uncover the weak points of bosses, power up quickly, recognize key characters, and locate the best eateries in every town. With his new expertise and shrewdness, he eclipsed the Hero's group and embarked on a mission to conquer the Demon Lord.