Just because Sacred Echoes is publicly released doesn’t mean the assets are free to be grabbed nonchalantly.
Even though Sacred Echoes was made on FE8 engine, Gamma himself made lots of original alterations. This includes the portraits. The fact that the work is of a pre-existing character is completely irrelevant.
As per site rules, you are required to obtain permission to edit before publishing edits of existing work; this permission is distinct from permission to use the work in question.
Either find a replacement for the Fernand hair, or credit @HyperGammaSpaces for the parts you used. This should apply to all media you’re going to use from other artists in the future. Consult The Rules if you are unsure of how things work here.