As daughter of the former demon lord, Mio's foster parents were slain by powerful demons after her life. Still seeking to slay her, Basara reveals himself as a member of the hero clan--an enemy of the demons--and vows to protect Mio as a member of his family.
The main purpose of a Master-Servant pact 
is to maintain the subordinate's loyalty.
Die Intention eines
Meister-Diener-Pakts ist es,
El objetivo principal del pacto
 entre maestro y siervo
El objetivo principal del pacto
 entre maestro y siervo
À l’origine,
le pacte d’allégeance sert
Lo scopo principale di un patto Servo-Padrone
 è assicurarsi la lealtà del subordinato.
O principal objetivo de um pacto entre 
Mestre e Servo é garantir a lealdade do Servo.
Настоящая цель договора господин-слуга — 
обеспечение подчинения слуги.