Shouldn't that be ٌرَفِيْق(rafeequn) and ٌرِفْق(rifqun) respectively for the two. Additional ي between ف and ق is not for case, but it is used to indicate that it is for adjectives, most of the time.

As 'rafiki' is N/N class, the same word is used for both singular and plural.

In some regions people say marafiki in others they say rafiki. In swahili there are a lot of regional differences.