This post has an updated solution of KDST 525, starting with a 3-fill and a rare remote pair. The bv scan has an irregular XYZ-wing, and the 6-panel features a long XY nice loop that illustrates the XY Railroad on the SysudokuTools page. An easy coloring wrap finishes.
In the bypass, the 3-fill up front is soon filled, but many await line marking.
On the line marked grid, you likely see the naked triple first, but there is a Sue de Coq where Sr9 contains 2(3+4)(6+7) and r8c4 has to supply the 6 or 7 and r8c5 can only supply the 3 or 4. That fills out the remote pair. The hidden unique rectangle is signaled by the corner 18 values and the sling along one side. Think of the inference from 8 being true in a corner being carried by the slink. It doesn’t work from 8r4c3.
Another hidden UR follows with two slinked sides and diagonal extra values. Actually,, there’s two. If the other UR value in the slink corner is true, the slink value is carried to the adjacent corners, wiping out the extra values in both.
Now the XYZ-map yields an irregular grouped 476-wing. 6r4c8 sees two toxic 6’s already, and is helped to the third with a grouped 6-chain.
Then the aforementioned nice loop, over the remote pair territory, adds two more bv.
The crayons come out, and the 6 removals turn 6r9c6 blue, and 4r9c6 green, trapping 4r1c6, wrapping blue.
Shut off the lights when you leave. Next week, it’s KrazyDad Super-Tough v.5, b.2, #5.
Systematic Sudoku 