I like that they've done something funky with the height in this bathroom, but you could also paint the top part of the walls and the ceiling it a bright or a dark colour, since you have the light and the height. It will visually bring the ceiling down, which will make it feel a bit wider too.
For storage ideas: boxes like in the pic below, or shelves along the entire width of the narrow wall above the toilet will a) give you storage and b) visually widen the space
A frameless glass panel, narrow but long basin and wall hung toilet would give a streamlined look.
I would use tiles with a graphic pattern on the floor and probably on the far shower wall too, to give interest and let the eyes follow the lines in the tiles. The other walls I'd probably tile with a large format plain white tile.
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Recessed lighted storage
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