Osananajimi to Sex Friend Keiyaku

Our secret relationship starts now... I'll be your sex friend because I love you! That's my choice... "You're fine with anyone right? So... that includes me too." Ayane loves Hikaru, her childhood friend who's one year younger. But she finds out that he has a sex friend!! "Don't get a 'girlfriend' so easily! I don't want to give Hikaru to anybody!" In order to be with Hikaru, she tries becoming a sex friend, but...?! (Source: Shogakukan, translated)