Jiburiru: The Devil Angel Makai Tenshi Djibril

One hot summer day, Naoto Kamino finally musters up the courage to reveal his true feelings for his crush, Manabe Rika. Unfortunately, at the same moment, a young boy named Asumo appears (though he refers to himself as the devil). He plots to kidnap Rika and will stop at nothing to obtain her - but Rika has a little secret of her own, she can transform and obtain magical powers during sex...