Idol☆Sister

1-5. Idol☆Sister (アイドル☆シスター)
Takano Ayaka is a successful idol that constantly gets voted as the most popular from her group, however for her things aren't exactly as she has a pretty big secret that involves her brother.... Well, it's more like a secret relationship as hinted by the genre.

Her brother, for his part, is a huge sis-con and is pretty happy as how things are going around "Aya is my Idol only", are his thoughts....

... Now, we wouldn't have a story if these two wouldn't face any sort of complications at some point, would we?

6-11. Risa
Ayasegawa Risa is a high-school student at Seika Gakuen, she is a respected oujo who is hailed as the school princess and is well liked for her respectful and modest personality along with her great looks. She is even the daughter of the school principal.

Risa has a "secret" though, and is that she can't forget the feeling of meeting her first love, someone who rescued her from drowning when she still was a kid. Unfortunately she can only remember "that she loves him" and the first kiss that they had (which was actually simple CPR), Risa however can't remember his face, voice nor name.... While fretting about how she can't graps the details of such important memory, we have that in her class a new assistant trainee teacher is introduced, and as soon as Risa sees his face more of her forgotten memories are starting to resurface....

ch. 12. Ura Manager no Oshigoto (ウラマネージャーのおしごと)

(Source: AniList)