something innocent like Shoutarou one of the character and not afraid to show or say his affection for the other character. Looking for shounen-ai preferably.

it isn't similar in regards to plot but the feel of it is kinda similar in my opinion. the manga Seven Days by Tachibana Benio. Even if it isn't similar it still is really cute!

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).