The Testament of Sister New Devil

Basara Toujo, a high schooler, suddenly finds his father remarried and heading abroad, leaving him to live with two alluring step sisters. To his shock the sisters are Mio Naruse, a demon lord in hiding, and Maria Naruse, a cunning succubus. A magical mishap binds Basara to Mio in a reverse contract, making him her master rather than her servant. What follows is a string of chaotic encounters that blend flirtatious humor with over the top battles as Basara tries to protect Mio from demon threats and fearless heroes. The arrangement pulls Basara into a world of rival factions, forbidden power and dangerous loyalties. It all plays out in a high school setting where caffeine and courage often collide.

The series premiered in 2015 as a TV anime adaptation drawn from Tetsuto Uesu's light novel Shinmai Maou no Testament, with art by Yu Kuraishiro, bringing the demon lord and her family into color. It is faithful to the source while adding action.

Among fans, the show is known for its bold mix of action and ecchi humor and for Mio and Maria as standout characters who drive the premise. It helped popularize a subgenre blend where domestic life collides with a hidden supernatural world.

Critics noted a lively pace and a tonal mix that leans into fantasy mayhem while leaning on light romance and rivalry. The show treats family bonds with a playful subversion of power and desire, asking how far loyalty and protection should go.