Stax, 8 bytes

à░_▓7jq○

Run and debug it at staxlang.xyz!

Unpacked (9 bytes) and explanation:

r{s]:{+k]
r            Reverse string.
 {     k     Fold string with block, beginning with the first element:
  s            Swap accumulator and character.
   ]           Stringify accumulator. Only does anything once :(
    :{         Wrap accumulator in parentheses.
      +        Stick element onto front of accumulator.
        ]    Stringify. Necessary for length-1 input :(

Stax, 8 6 bytes

-2 thanks to @recursive!

çΔ \Γ]

Run and debug it at staxlang.xyz!

Unpacked (7 bytes) and explanation:

Mrks:{+
M          Transpose array. This turns a string into an array of length-1 strings.
 r         Reverse string.
  k        Fold array using the rest of the program as a block:
   s         Swap. This puts the accumulator on top of the current element.
    :{       Wrap in parentheses.
      +      Concatenate.
           Implicit print at end of program!