I'm a bit weirded out by mirrors in kitchens. My sister in law has a mirror backsplash on more than one wall in her kitchen including two walls that face each other with the main food prep area, sink area and a counter area between. I can't handle seeing kitchen mess infinitely repeated and disappearing off into the distance. It's a look for tidier people than me that's for certain.

Please post a pic of the whole room. It might take several pics to show the room. You can do so in the comment section here. We are visual people so photos and a measured diagram showing dimensions help. Thank you for mentioning that it is a rental so we know right from the beginning that you aren't moving anything :)

Keep whatever you add uncomplicated and make sure you don't block the light. Consider adding some small Tiffany style sun catchers attached to the windows with suction cups to add your choice of color or vibe to the room. This holiday time of year, you can usually find some good suction cups at Dollar Tree. The sun catchers are small enough to be easily stored so they can be changed out according to your mood or the season of the year or the holiday or the likes/preferences of the person you're celebrating. Suncatchers can help keep birds from crashing into your windows. Selectively collecting them -- only what you'll actually use -- can be fun -- something to look for not just new and on line but also in "used stuff stores": antique and thrift stores such as Habitat for Humanity and Good Will and Salvation Army, etc.. You may find you end up putting a few in windows in other rooms as well.

jennifer, if you want to do a slat wood wall (there are a lot of tutorials on how to do it. it's mainly 1x1 or 1x2 wood 'sticks' that are 8'-10' tall. you could use fir and stain them. or you could paint them black. or, if you have a bigger budget, get walnut or something similar. walnut you'd only have to oil. it's a red wood. just a medium brown tone that would great w/the floors. if you like a more natural color, look at 1x2 white oak pieces. (any lumber place should have them) a satin oil finish is all you would need. those can also be stained a walnut color. (oak is cheaper than natural walnut this one is actually poplar that they painted. if you're goign to paint, use poplar wood https://brepurposed.porch.com/2020/01/20/diy-wood-slat-walls/ so, you'd paint the wall black, and attatch the slats. this looks like Alder that has been stained a darker walnut stain. here's the lighter stain color. you could also get plywood and rip it to 1" pieces (however, plywood and lumber have skyrocketed this last year. it's ridiculous what a sheet of plywood costs.) https://simplyalignedhome.com/affordable-slat-wall/ I think if you even did the entry niche w/some type of slat or design would look great I'd go all the way down, and prop paint it black, or do the wall in black and do walnut wood pieces. or, I like this too. find a cool black/white/gray piece of art, something more vertical, and hang it. bring in some bright color stools to fit under the marble. bring in a entry way rug that matches or make a cool design and use that as your art element in the niche (I actually made a headboard similar to this one out of scrap wood pieces. came out really cool) over on the dining wall, you could easily do a living plant wall