You don’t need to worry about having a swimsuit as baths are male/female and you wear provided outfits in common areas. Also if you have a tattoo they sell you flesh colored temporary tattoos to cover
Great onsen (public bath) with an outdoor and indoor bath, 2 massage spots, massage chairs, dining, and so much more. Don't miss this if you're around Shinjuku, a great way to relax and unwind.