Shuu Hinamori is Amu's older cousin.

He is an one-use, anime-only character that appears in episode 35.

He still has a Heart's Egg within him, and because of that he can hear Guardian Characters when they talk next to him.

In the anime, he was Amu's first love.

In a flashback, he was shown taking care of a younger Amu, and always baked for her. Though she acted like she didn't care, she actually liked his baking.

(Source: Shugo Chara! Wikia)