Characters are sometimes added at the voice actors ' convenience .
Characters are sometimes to fill in gaps that occur for each installment 's story ; this happens with Duck King in The King of Fighters XI and Ryuji Yamazaki in The King of Fighters ' 97 .
Characters are sometimes added at the voice actors ' convenience , or to fill in gaps that occur for each installment 's story ; this happens with Duck King in The King of Fighters XI and Ryuji Yamazaki in The King of Fighters ' 97 .