If cosplaying other FFXIV characters they'd cosplay Thancred. They like cool coats and it'd be a fun way to tease him. If any series is fair game then pre-Heavensward Kaoru would have cosplayed 12 year old Naruto. Feral confident energy with a big appetite. Post-Heavensward Kaoru would cosplay Xiao from Genshin Impact because they would feel a kind of kinship with him over their own past mistakes and regrets.