I've been super satisfied using the Fujifilm XF 18-135mm f/3.5-5.6 R LM OIS WR for travel. Honestly, it works well even if it is an older design, and you can find used copies for a total bargain right now. I have no complaints about the reach or the weight on the X-S20. It is definitely worth it for a Japan trip!

Like someone mentioned, the 18-135 is definitely showing its age. Ive been shooting Fuji since the original X-Pro1 and over the years ive learned that travel photography is 90% about reliability and 10% about pure sharpness. You dont want a lens that creeps when youre walking through Kyoto or one that fails the moment it hits some light rain. Honestly, the 18-135 was a workhorse back in the day, but its just too soft on the edges for the newer sensors. In my experience, the Fujifilm XF 16-80mm f/4 R OIS WR is the sweet spot for the X-S20. Its what I take when I cant afford a gear failure.

• Constant f/4 aperture: This is huge. You dont have to worry about your exposure settings jumping around as you zoom in for a shot.
• Better Weather Sealing: Japan can be unpredictable. Ive used this lens in heavy mist and light rain without a single hiccup.
• The OIS is insane: When you pair it with the IBIS in your X-S20, you can basically leave the tripod at home for night shots. I once brought a heavier setup to Hokkaido and by day three my neck was killing me. The X-S20 is a small body and if you go too big, the balance feels totally off. The 16-80mm fits the ergonomics way better than the 18-135 or some of the bulky third-party zooms. If you really need more reach later on, you could look at the Fujifilm XF 70-300mm f/4-5.6 R LM OIS WR, but for a one-lens solution under 900 bucks right now? Stay with the 16-80. Its built like a tank and wont let you down when it counts. Wait, I forgot to mention the zoom ring... its way tighter than the 18-135 copies I've used lately. No lens creep is a godsend when the camera is hanging off a shoulder strap all day.

^ This. Also, looking at the two paths suggested so far, you're basically choosing between total convenience and modern optical performance. Over the years, I've tried many of these combos and found the old 18-135 is definitely showing its age on the newer 26MP sensors. It works, but if you're planning on printing anything from your Japan trip, you might notice the corners getting a bit mushy. In my experience, the real sweet spot for Fuji travel that people often overlook is the Fujifilm XF 16-80mm f/4 R OIS WR. You lose some reach on the long end compared to the 135, but having that 16mm wide angle is absolutely crucial when you're tucked away in a narrow alley in Kyoto or trying to get a full shrine in the frame. That extra 2mm on the wide end makes a bigger difference for travel than the extra 50mm on the telephoto side. Plus, the constant f/4 means your exposure wont jump around as you zoom, which is a major plus for the video capabilities of that X-S20. Since you're watching the budget, you can easily snag that lens used for around $500. This leaves plenty of room in your $900 limit to grab a small prime like the Fujifilm XF 23mm f/2 R WR for night walks in Shinjuku. Carrying a massive all-in-one zoom sounds good until you're ten miles into a walking day... honestly, your neck will thank you for keeping it light and modular.

I spent weeks analyzing MTF charts and linear motor specs before my last trip! Honestly, the engineering in modern third-party zooms is basically amazing now. I love how sharp they are. You should definitely look at any of the glass from Tamron. Their optics are fantastic and the weight savings are a total game changer. Just go with their stuff for Fuji and you wont regret it!