Looking for a comedic shoujo I forgot the title of

It's about a pretty stupid girl and a tsundere kouhai who likes her. (Set in high school.) He mostly teases and makes fun of her, she's oblivious (in a funny way). She has blue hair, he's blond. I think the manga title is just their names. Think "[name] to [name]" as the title format.

The gag I remember best is a comedically raunchy foreigner named Cathy they keeps showing up in foreign films and English learning CDs and books. I think her first appearance is in a film called something like "the story of two people who met in the rain." I cackle every time she shows up, to the point that I care more about her than the romance. Please help me find her 🙏