Would it be odd to just have a pane of glass made for the space with 1 awkward angle? Adding a photo of the adjoining wall. Another window dilemma.

I would get two wide short windows that will fit ...not slanted. Might have to have them special made but I doubt it. Other choice is one window where the roof is not slanted.

Just put a long horizontal window in the space that you have, that doesn't open. As long as it isn't looking out the front of the house, I don't think it matters that it doesn't match the others.

How it looks on the outside if the house is just as important as the insid. You need to examine the exterior.