What Shugo Chara episode is Amu and Ikuto in the rain?

The episode you're thinking of is Episode 42: "Amu's Resolution! Ikuto's Feelings!"

In this episode, Amu and Ikuto get caught in the rain after a chase scene with the Easter Company. They end up taking shelter under a tree, and Ikuto opens up to Amu about his feelings for his guardian character, Yoru.