Seikou Tenshi Yarinikuru

"When you turn 16, let's 'agape' together.." Ichizu Michisada, a young man who often dreams of having made such a promise to someone, is visited by Yarinikuru, a silver-haired, red-eyed, panty-flashing angel. According to her, she was sent from the heavenly realm to have "agape" (sex) with Ichizu! (Source: Comic Alive+, translated)