Sono Munou, Jitsu wa Sekai Saikyou no Mahoutsukai: Munou to Sagesumare, Kizoku-ke kara Oidasareta ga, Gift "Tenseisha" ga Kakusei shite Zense no Nouryoku ga Yomigaetta Chapter 12
That Incompetent Is Actually the World's Strongest Wizard Chapter 12
There might be spoilers in the comment section, so don't read the comments before reading the chapter.
Sono Munou, Jitsu wa Sekai Saikyou no Mahoutsukai: Munou to Sagesumare, Kizoku-ke kara Oidasareta ga, Gift "Tenseisha" ga Kakusei shite Zense no Nouryoku ga Yomigaetta Chapters