ANE LOG: BIG SISTER MOYAKO'S NEVER-ENDING MONOLOGUE

When Konoe Moyako and her little brother, Akira, were young, he said he wanted to marry her. Naturally, Moyako decided that her little brother was a complete pervert who was obsessed with her. Now that they're both teenagers, Moyako is convinced she needs to "rehabilitate" him. However, it seems that the "perversion" is entirely in her imagination, and she can't seem to help turning completely innocent situations into creepy ones in her mind! — Description from AniList community (anilist.co).