Self-mate in 28, with cross-checks

In a "self-mate", white plays first, but he is trying to force black to checkmate him, not to give mate.

Therefore, although White may mate in one by d8=Q, he is not interested. He goes about a particular sequence of moves, forcing Black to make "only" moves, as one rook climbs down the ladder, giving check and covering check continuously. It dies on g2, Black making tempo moves with h-pawns. The other White Rook plays up the same ladder, giving check and covering check, sacrificing itself symmetrically at b7, even as an under-promotion gives White tempo moves to allows Black to mate.

Count the number of checks.

Themes with multiple cross-checks are called Brede checks, a term introduced by Alain C. White of an Ellerman three-mover in a Good Companion folder.