After ending the battle against Zolgia, Basara regains his peaceful life with his two little sisters, Mio, the daughter of the previous demon lord, and Maria, her little sister who's also a succubus. As Basara pursues the preparations for the sports festival at school, one day he's attacked by a person being manipulated by magic. Recalling the strange gaze he felt at school, a suspicion of his begins to grow...
They thought Onee wasn't enough to 
handle observing things on her own.
Sie waren der Meinung, Onee wäre der
Observationsaufgabe allein nicht gewachsen.
Consideraron que Yuki no podría realizar 
su labor de observadora sin ayuda.
Consideraron que Yuki no podría realizar 
su labor de observadora sin ayuda.
Vu que les pouvoirs de Yûki 
ne sont pas suffisants,
Hanno ritenuto che la sorellona non fosse
 in grado di gestire la situazione da sola.
Eles acharam que a Onee não era o 
suficiente para o serviço de observação.
Они решили, что сестре одной не справиться,