The Testament of Sister New Devil

Shinmai Maou no Testament
新妹魔王の契約者(テスタメント)

Sequel

manga

High school student Toujo Basara’s life has taken a turn for the strange. Although hesitant about his father’s sudden decision to remarry, he can’t deny it comes with a couple perks—drop-dead gorgeous step-sisters…who also happen to be members of a demon clan! Mio Naruse is a Demon Lord and Maria Naruse her succubus servant. Chaos and passionate antics ensue as Basara gets acquainted with his new demonic siblings, trying to protect them from dangerous demon rivals and struggling to keep up with their lusty, devilish appetites. (Source: Seven Seas Entertainment)

Adaptation

novel

When his oddball father suddenly decides to remarry, high school student Toujo Basara is about to acquire some very peculiar new family members. Enter his new seductive step-sisters, Mio and Maria. When Basara discovers that one of his step-sisters is a succubus and his other a recently crowned demon lord, all hell breaks loose! Basara is almost forced into a contract with his demonic sisters where he would act as their eternal servant—but something goes wrong. Instead, a reverse contract is formed, and Basara becomes the master. Between fending off their seductive advances to coping with the attacks of rival demon contractors, Basara has a big learning curve if he is to survive. (Source: Seven Seas Entertainment)