Originally Posted by Ani_BEE
It sound like the red fabric wasn't pre-washed when you made it. Red will always bleed which is why you want to use synthetic fabric for it as much as possible.
had the same issue with my Mami cosplay. I removed all the trim and coloured fabric. Bleach the white pars with stain remove (Rit makes one). Wash the trim/colour fabric separately and then sewed it back together.
They bought it, since the OP said the received the costume the other day.
Maybe you could try using a stain stick/tide to go on the white parts? I'm not really an expert on fabrics. Try maybe spot-bleaching it? Sorry I couldnt be more of a help.