What do you think Sebastian's thoughts about Joanna?
You mean about Joanne Harcourt? Sebastian probably doesn’t think too much in particular about him. To Sebastian humans are more like insects anyway. Some of them are useful to him and I guess Harcourt belongs to that group. In the Weston arc he was useful because Sebastian got information about Maurice Cole from him. And now in the current arc Harcourt was useful as part of Ciel’s boy band. Sebastian surely noticed that Harcourt adores him and used that in order to convince him to help.