The character for Aki means "Autumn", and Shizuha "quiet leaves."
It makes very much sense for Shizuha to be the older sister who is the goddess of turning leaves as the leaves change in autumn before the harvest.
According to Symposium of Post-mysticism, Shizuha is somewhat jealous of her sister's bigger popularity with human because of her ability.
Because she and her sister were ranked the lowest of the Windows characters in a year's annual Touhou Popularity Poll, there is a running joke in Japan that they are "original characters" with negligible presence in the games. There is a doujin anthology project dedicated to the Aki Sisters, perhaps to compensate for this.
On her character portrait, the leaves on her head roughly resembles a crab if they are seen as a single piece rather than two. This occasionally leads to her being associated with one, the leaves on her head being replaced by one, or herself replaced by one in fan works.
If taking an article in Symposium of Post-mysticism as a guide, her personality is pessimistic; she believes that the end (of the year) will always come. Outside of autumn, she does nothing, and is even prone to disappear.