well casual has no ranks, n so theres non shown. you can face everyone no matter which rating he/she has in ranked.

ranked is splitt into ranks n different leagues. there are 5 leagues show by the color of the avatars border

bronze ( brown, no wings attached ) with ranks 10-1
silver ( gray, small wings attached ) with ranks 25-1,
gold ( "gold", larger wings ) with 40-1,
platinum ( silver, even larger wings ) with ranks 50-1
diamond ( white square border, largest wings attached ) with ranks equal to players that made it this far.



if you want to guess how experienced your rival is titles n badges might help. since they unlock by play time n certain tasks that sometimes requiere diamond-cards.

the title "tetsu-adapt" for example needs lv9 in smithing, a tetsu-katana ( diamond card ) and a full-tetsu ( emerald card )

the title "one punch legend" needs lv9 in attack and a gluttonus behemoth ( ruby card )

"to the death" is a low lv title that requieres a base card only but stills its kinda impossible to make it in a regular way, ppl with that one were either extremly lucky, greedy or can prefectly read their rival. in other words quiet dangerous.