One of the things I like about following long-running manga series is seeing how the art evolves over time. I think one of the best examples of this is the shoujo classic Boys Over Flowers. Here are some scans from the first volume, where Tsukushi makes an impression on Tsukasa by kicking him in the face:
Tsukushi’s kick reminds Tsukasa of his older sister:
And much much later in volume twenty-six, they reach a turning point in their relationship: