Prologue

What if Issei had an adopted sister? What if Vali was mates with Issei's said sister? Serenity Hyoudou is the adopted sister of Issei Hyoudou. Serenity and Issei were inseparable. After Rias Gremory moved in, Serenity was being pushed aside. She had enough of being ignored and ran off. She decided to go to Azazel and ended up running into Vali Lucifer on the way. Vali finds her interesting and has no idea that she is his rivals sister. Vali wanted a chance at a normal life so he hung out with Serenity and Azazel in his free time. What happens when he starts to develop feelings for the 'human'?