"...I was attacked by O Toyo.":
The cat of Nabeshima is what Chiyo is refering to. The legend about this cat features a concubine of the name O Toyo, to which this cat impersonates. It would seem the easiest way to refer to this cat. In the legend, the cat is described as being giant, and as having two tails. This chapter title is also in reference to this legend.