Rotate face but stay orthogonal

I recently stumpled over a simple task, but I couldn’t find a proper workflow:
How do I create an exact rotated edge (see selection) where outer faces / vertical edge loops
stay orthogonal.
I hope there’s an obvious solution, but I just couldnt find it. Thank you for your tipps.

The command is called “Shear”. Look on status bar for options (X, Y axis, angle (radians, can write “pi/4” e.g.)).

Edit: Argh, that’s Space bar search or some 5-fingery shortcut hard to memorize anyways.

I can’t quite figure out what you are asking. But that never stops me from making a guess so I will say you are calling it rotate but you are thinking of SHEAR.
Press shift ctrl alt S and then press either x or y to determine the shear direction. Note that this operation is window dependent so I recommend using one of the axial ortho views at first to keep things understandable.

edit: Arggh beaten to the punch by Eppo while I was making some useless graphic attachment. But at least I remembered the shortcut. only 4 fingers!

Great! That was the quite function i was looking for.

Thank you very much eppo & DruBan