User blog comment:B214/Volume 23 discussion blog/@comment-185.112.105.215-20170419115644/@comment-31137559-20170420204529

And Koneko showed no affection for Issei until Volume 5. It's possible for someone to realize feelings for someone much later even if it seemed that had no affection towards said person before. It's not like every girl in Issei's harem fell in love with him at first sight. Look at Elmenheide. It's not impossible for Sona to have developed some feelings for Saji.