In the film, Taki and Mitsuha also keep forgetting each other because they switch places in their dreams, and, as Mitsuha's grandma puts it: Treasure the experience.
Cronin explains that this tradition involved taking the shamrock that people wore all day, and placing it in a glass of whiskey or beer before drinking it.
Now the rainbow faded and the balls of light reunited and merged; they had formed a great shimmering shamrock, which rose up into the sky and began to soar over the stands.
But his first love is a type of marine creature called trilobites that once teemed in Ordovician seas but haven't existed for a long time except in fossilized form.