Just double checked, it's not even moving to diagonally adjacent boards to create an opening, the opening is purely laterally. Movement through time is only through available boards with the "only 1 move per board" rule and the "1 move = 1 time skip" rule. Kronii is black in this game and she has her bishop in at the board labeled "Present". Her 1st movement backwards in time requires a lateral direction, which is down, and it is actually 2 boards back in time because the timeline behind that belongs to Ame. Her 2nd movement does the same thing but there is an opening in that "2 Moves" timeline as the Pawn has been moved forward and the Knight hasn't been moved into its place yet. The "3 Moves" is her Bishop simply moving downward a 3rd time to capture the King. Note the boards have a black outline indicating that she can move to those timelines.
EDIT: The "check" was created because of an opening caused through the passage of time. Even though Kronii had already had her Bishop at its "Present" position during the "1 Move" board, it wouldn't have been able to check if she simply moved it during her previous turn as it would be blocked by the Pawn in the "3 Moves" board.
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