User blog comment:Crimson and Darkness/Volume 24 discussion blog/@comment-73.57.25.92-20171118152541/@comment-83.57.140.251-20171118163443

Look the cover of this volume... Of course.. According the spoiler first Koneko kissed Issei and then Kuroka, even in the sister images seems that both are in the bath with him..

In EX, the sisters daughters born at the same time, they made a trio, sure.