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...
I'll show you which of us is more mature.
Ich werde dir zeigen,
wer von uns reifer ist.
Te dejaré claro quién es más madura.
Te dejaré claro quién es más madura.
Je vais t’apprendre 
qui est la plus mature !
Ti faccio vedere io chi è più matura tra le due...
Eu vou te mostrar quem
 de nós é mais madura.
Узнай же, кто на самом деле взрослый.