Day before yesterday I saw a rabbit, yesterday it was a deer, and today it was you.
Kotome says this multiple times throughout Clannad and I had no idea what it means. So I turned to my handy, dandy, google search bar. Turns out, the line is from a short science fiction work called “The Dandelion Girl”.
On the surface, Julie, the girl from the story, is simply noting what she’s seen each day. The significance is that each day, what she sees becomes more and more spectacular. She repeats this to another character named Mark. It symbolizes how each day, their relationship, or love, has grown more and more spectacular.
To put it another way, it’s kind of like Westley telling Princess Buttercup “As you wish.” each day.
What makes this better is that Kotome loves to read, and has probably read the story so she understands what this line means. Meanwhile, Tomoya is Princess Buttercup and takes a while to catch on.