Slant cubby with a tall back pillow for a bedroom window seat, could make it storage functional and comfortable. Details of the window seat-built-in bookcase, storage under seat, piping on cushion, pillows (House of Turquoise: Lou Lou's Decor)
Creative ideas for using the space under the stairs. Brilliant use of space! Not nuts about the bathroom idea though. I guess if you had a tiny home with no main floor powder room it could be workable.