Both of these have a lot of similar plot elements:
1) Sexy lead male who is also super famous. They are both sons of very wealthy men and their mistresses. They also go to highschool with the girl.
2) Normal highschool girl who has a penchant for writing erotica. She is inspired by the guy for much of her writing.
3)Both guys have a super strong need to protect Aine/Shiina from whatever craziness they get themselves in to.