Seconding Seven Days and adding Hana no mizo Shiru, Arikawa is probably the most adorable and straight-forward character I know. Since both are famous, if you already have read it, I could try searching more for you. Other mangas with great characters I love: Doukyuusei, Kusakabe is very open about his feelings. Rutta to Kodama, but it's a yaoi (not a very graphic one, but still...) Junketsu Drop is not exactly what you're looking for, but still very cute and Misato is adorable too. Slow Starter (ICHIKAWA Kei) is a good shounen-ai too, but it takes some time to develop into something and it's not exactly what you're looking for (more shy characters).