Like Gensokyo, Ireland has a god of agriculture. His name is Bres. As with all mythology, different portrayals of him exist, ranging from him being a tyrant to being kind and noble. But regardless, he makes the crops grow and the cattle give milk, and he is credited with teaching the Irish the secrets of farming.
However, the Irish harvest festival, “Lunasa”, is not named after Bres, but after Lugh. Lugh is known as “the Long-Handed” because of his mastery of all arts: music and dance, painting and sculpture, architecture and smithing. The band Lunasa takes its name from him, and by extension, so does Lunasa Prismriver.
The reason the harvest festival bears Lugh’s name is because Bres taught the Irish how to farm only because Lugh defeated him in battle and forced him to do so.
One of the older versions of the Autumn Children script had Lunasa raised as a follower of Lugh (hence her name). She wanted to meet Shizuha because she missed the gods of Ireland and Shizuha was the autumn goddess who reminded her of Lugh. Through Lunasa’s help, Shizuha discovered that she was the goddess of art, not just of the autumn leaves.
This was taken out because of how long it would take to write, how it would make Shizuha much more awesome than she actually is, and how it would conflict with the central theme of the strength of ordinary people. There is nothing Shizuha teaches Laurie that couldn’t have been taught by any artist with enough experience.
Autumn in Ireland is not only the season of the harvest. It is also the season for appreciating beauty: the beauty of nature, created by the hands of god, and the beauty of art, created by the hands of men.