The Testament of Sister New Devil #1

Basara Tojo tries to keep to himself in his quiet life—until his father brings home two mysterious girls: Mio Naruse, a sharp-tongued teen, and her younger sister, Maria Naruse. What starts as an awkward household adjustment quickly unravels into something far stranger when Basara realizes the girls are demons with a deadly mission—and that he might be the key to their plans.

When Basara Tojo awakens to powers he never knew he possessed, he unwittingly drives Mio Naruse and Maria Naruse from the house they’ve come to call home. Haunted by guilt and the mystery of his father’s past, Basara sets out to find them—only to discover Mio and Maria under siege by rival demons, their fate now inextricably tied to his own.

When Maria attempts to bind Basara and Mio with a protective Master-Servant spell, her magic misfires—turning Mio into the servant and Basara into her master, with unforeseen consequences for their bond. Now, the balance of power shifts in a way no one saw coming, as Mio’s loyalty and Basara’s responsibility are tested in ways neither expected.

When a childhood friend from Basara’s past returns to school—her presence both a nostalgic echo and a quiet threat—old bonds stir and new tensions rise. Now, as Mio and the others navigate shifting loyalties, the space between trust and reunion grows thin, and the past refuses to stay buried.

In the shadow of shifting loyalties, Maria’s schemes unfold as she leans on Mio’s charm to pull Basara back into their world—while rival demons circle, each eager to claim Mio’s throne and end her line. With Basara caught between past bonds and uncertain trust, the space between reunion and loyalty grows thinner than ever.