First of all, it’s an icon problem.
The cavalry icon is stored immediately after the attribute icons.
Also, if you are using the Japanese version (FE6, FE7J, FE8J), you also need to expand the table of attribute names.
This is not yet supported by FEBuilderGBA.
Well, the icons aren’t a problem. Just expand the table from 0x07 to 0x0C (example if you want to add 2 new affinities) and don’t use the slots from 0x08 to 0x0A. These slots use the Calvary, Pegasus and Wyvern Icon. Slot 0x0b uses the member card as icon (If I’m not mistaken), which you can use. Then give the Member Card a different Icon.