fish-shell-pure, 173 bytes

Result

AC

Duration

1323ms

Code [DL]

read s
set t (string split \  (string match -nr T $s))[1]
while read p
echo $s
set k (string trim -r $p)
[ $k ]&&echo $k(string repeat -n (math $t-(string length $k)) @)
end

stdin

                        T                         
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
               K                                  

stdout

                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
                        T                         
               K@@@@@@@@@

stderr

strace