Muhyo to Rouji no Mahouritsu Soudan Jimusho: Mazoku Magushi-hen

Magical Law (Mahouritsu)... its purpose is to punish spirits who have harmed human beings or have committed wrongdoings. Muhyo, who is a genius practitioner of Magic Law and the youngest Executor ever, and Jirou Kusano (Roji), Muhyo's crybaby assistant who hardly ever supports him, investigate mysterious blackouts and spiritual phenomena that have been occurring in the city frequently. Moreover, those blackouts involve a person called the "demon magician," who creates forbidden tools. As they investigate further an ominous shadow approaches the two...!? After solving numerous cases and mysteries in the past, will Muhyo and Roji succeed again? (Source: Shueisha, translated)