#C, <s>139</s> 138 bytes <!-- language: lang-c --> char*s="aiueokstnhmyrw";i,j;k(char*v){for(;*v;i||(i=j))j=strchr(s,*v++)-s;j=i<4?i++:j<4?j-~(2520%i&3):!++i;printf("%c%c",s[i],i<5?:s[j]);} [Wandbox](http://melpon.org/wandbox/permlink/9yDwtMxRblT5SAv9)