java, 160 bytes

Result

AC

Duration

1637ms

Code [DL]

class A{public static void main(String[]a)throws Exception{for(int d=1,c;(c=System.in.read())>0;d=c>83?1:(d-c%2*51+1)%51)System.out.print(d<1?"A":(char)c+"");}}

stdin

                                         T        
                                                  
                                                  
                                                  
                                                  
                                                  
              K                                   

stdout

                                         T        
                                         A        
                                         A        
                                         A        
                                         A        
                                         A        
              KAAAAAAAAAAAAAAAAAAAAAAAAAAA        

stderr

strace