What do chess and wordoku have to do with each other? - Clue Thirty-One

Question

_{<<---First clue
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(?)}

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"Aha! That's it," you exclaim, still holding the papers. "The answer is obviously [redacted]."
Having figured out the answer, you start looking over the rather bare-looking desk, still swiveling in the chair. Then, behind you, you hear a click. You stiffen. Slowly, you turn around, thinking uh-oh. Before you get all the way around, though, there's a loud SNAP and the legs on your chair snap.

You tumble on the floor, dropping the papers, covering your head with your hands. When nothing happens, you slowly stand up, looking all over the room. You don't see what may have made that click, but you do see that there is something on the ceiling.

You stand up and crane your neck. Squinting, you struggle to make it out. It appears to be a Sudoku board, along with four chess board. An odd combination, you think. Scanning the ceiling, you see a line of what appears to be instructions on the right:

What does chess have to do with sudoku? You'll see. Solve the sudoku, and then figure out what makes each chess board so... unique, let's say. I daresay that'll be impossibly, essentially. Can you figure out what you have to do after that? Good luck, Clue hunter.
-P. Oh

Here are the chess boards and sudoku board:

_{Boards generated with lichess. Sudoku puzzle originally generated by http://www.sudokuweb.org.}

Answer 1

The answer is:

LILY

This is obtained from:

Taking the most obvious* error on each chess board and using the letter at that position in the solved wordoku.

*Ordered by:
 • A piece in an impossible location (without considering other pieces);
 • Duplicate pieces;
 • A piece in an impossible location (taking other pieces into consideration).
Tie-breaking is done by using the one with more errors.

For the first board:

The pawn at G8 is in a position that is impossible for a Pawn. This corresponds to the letter L on the wordoku board, as solved by Beastly Gerbil. No other piece is in an impossible position when considered by itself.

For the second board:

There are two white Kings and two black Bishops on black. Also, several Pawns are misplaced without an amount of pieces missing to make it possible. The Kings and Bishops are the only ones that are duplicates.

The King at D7 is the only one of these that is also in an impossible position (double check). It corresponds to the letter I on the wordoku board.

For the third board:

The Pawn at F1 is the only piece in an impossible position without considering other pieces. That location is the letter L on the wordoku board. (This letter was given in the original board)

For the fourth board:

The white Bishop at F3 is the only piece out of place. The white King and Rook can reach those positions by castling. F3 is the letter Y on the wordoku board. (This letter was also given in the original board)

Putting these letters together, we get the solution:

LILY

Answer 2

Solution to the sudoku:

Apep found the final answer:

Taking the most obvious errors on the chess boards and matching the position of the piece to the chess board gives G8, D7, F1 and F3 which corresponds to the final answer LILY.

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STEP 1: Start small

The following letters can be solved simply with the letters already given:

STEP 2: Make the BED

Now B, D and E can be completed:

STEP 3: I SPY, with my little eye...

And then S, P and Y can be completed:

STEP 4: Complete the square ^{$\small{\text{(Not the quadratic)}}$}

And now finishing off is easy:

Final solution:

No idea about the rest though...

Answer 3

Incomplete/Partial Answer

If we look at the chess boards, it becomes clear that

some of the pieces are in impossible places

So let's look at their positions, shall we?

On Board 1:

Black pawn on G8 (Pawns can't move backwards, obviously)
Possibly, the Rook on H7? (The aforementioned pawn should be there, so the Rook shouldn't be)

On Board 2:

White King on D7 (Should obviously be a Black Pawn)
Black Bishop on A5 (Black still has the black-square bishop in it's starting position, F8, so this bishop should be on a white square)
Two White Pawns on C5 and F6 (No black pieces have been captured, so these could not have changed columns yet) White Bishop on E4 (Pawns on E2 and G2 haven't moved, so this piece should not have been able to leave starting position on F1)
Possibly White Rook and King on F1 and G1? (As mentioned in previous, Bishop should still be there, stopping them from castling)

Board 3:

White Bishop on G5 (Pawns on B2 and D2 haven't moved, this piece couldn't have left from C1.)
White Pawn on F1 (Again, Pawns can't move backwards)

Board 4:

White Bishop on F3 (Again, pawns in front of it's starting position haven't been moved, this piece should not have been able to move)
Again, possibly Rook and King on F1 and G1? (Again, due to Bishop should still be on F1.)

All of them together (Maybes added afterwards in brackets):

G8, D7, A5, C5, F6, E4, G5, F1, F3 (H7, F1, G1, F1, G1)

I tried to take these to be positions on the competed Sudoku grid (Refer to Gerbil's answer for the completed grid)

G8 - L
D7 - I
A5 - I
C5 - S
F6 - I
E4 - E
G5 - P
F1 - L
F3 - Y
H7 - Y
F1 - L
G1 - E
F1 - L
G1 - E

So I had

LIISIEPLY (YLELE?)