Nee-chan no Tomodachi ga Uzai Hanashi

Nao Misumi, a first-year high school student, has known Sena Ikuta—his older sister Rio's best friend—since he was in elementary school. A self-professed "sister's boy," Nao has always found Sena's overfamiliar attitude insufferably irritating. Loud, scatterbrained, and utterly incapable of respecting personal space, she should be nothing more than a thorn in his side—yet somehow, he has never truly been able to hate her. After all, she has always looked after him just as devotedly as she looks after Rio. She's a complete airhead, impossibly carefree, and her grasp of personal space is broken beyond repair. By all rights, she should be nothing more than a nuisance to him—and yet... "At first, I definitely hated her. She was loud, and she always took the things I held dear. So why is it that now—?" Even as he grumbles about her endless habit of calling him "Lil bro," he finds himself unable to simply leave her be. When exactly did this "annoying" presence in his life become the one person he can't look away from?