Cassia is a strong and steady crane, who moves cargo carefully from ships onto the trucks of waiting trains (albeit not without the occasional scrape). She enjoys working to a musical rhythm, such as the Batucada and Bossa nova tunes of Brazil. When there is no music, she will find her own, from sounds all around the docks.
Although Cassia is a Brazilian crane, she is actually based on a Chinese portal crane built by Xinxiang Kehao Machinery Equipment Co., Ltd, which is extensively used to load and unload at ports and material handling at shipyards and metallurgy industry. Carly is also based on this crane.
In Big World! Big Adventures!, Cassia was painted red with yellow hazard stripes along the underside of her body. Her cab roof is blue along with her safety rails and access steps.
As of the twenty-third series, Cassia has been repainted. She is now painted orange and her cab roof is orange instead of blue, though the yellow hazard stripes underneath her body remain along with the blue safety railings and access steps.