Been shooting Fuji for a decade and honestly, the 27mm is just a bit too narrow for those tight Tokyo alleys. Id grab the Fujifilm Fujinon XF 18mm f/2 R instead. Its basically a pancake too but gives you that extra breathing room you'll definitely want. Its light, fits your budget used, and looks great on the X-T5... trust me, you'll want the wider view for Shinjuku.

I would suggest being cautious with weight. Consider:

• Fujifilm XF 16mm f/2.8 R WR: light and wide.
• Sigma 18-50mm f/2.8 DC DN Contemporary: fast but versatile. Make sure you dont overspend.

Id be a bit cautious about going too narrow in Tokyo, those alleys are tighter than you think. Since youre using an X-T5, you might want to consider these technical trade-offs for reliability:

• Fujifilm XC 15-45mm f/3.5-5.6 OIS PZ: Honestly, ignore the plastic build for a sec. It weighs literally 135g, which is basically nothing. The 15mm wide end gives you a much better field of view for Shinjuku than the 27mm pancake. Just make sure to carry an extra battery because the electronic power zoom drains power a bit faster than a manual lens.
• Samyang AF 12mm f/2.0 X: I would suggest this if you want something faster for night shots. Its 213g and has a solid f/2 aperture. Be careful tho, it doesnt have a physical aperture ring, so youll have to use the front command dial on your camera body. Just keep in mind that the XC lens isnt weather-sealed... if it starts pouring in Ginza, you gotta tuck that gear away fast or it might get glitchy. The Samyang is a bit more robust for the price imo.

If youre worried about the 27mm being too tight, the Fujifilm XF 23mm f/2 R WR is a solid middle ground. Its wider for those Tokyo streets but stays pretty compact on an X-T5. Plus, the weather sealing makes it more reliable if you run into rain. It usually hits that 400 dollar used budget pretty easily too. Snappy autofocus is a huge win for street shots.