Murasame-kun no Tawagoto

Chika has always seen Murasame-kun as a rival who manages to constantly piss her off. While wondering out loud to herself, her sister whom overhears Chika, gives her a perfume necklace which supposedly able to capture a guy's heart. The next day, Chika bumps into Murasame-kun and spills all the perfume. As she begins to apologize, he suddenly asks her out!?

(Source: Intercross & Shoujo Crusade)