TL;DR: Canon RF 24-105mm f4L IS USM is the safest and most logical choice. It offers the reliability and range you need without overspending. I have been very satisfied using this lens for a while now. Methodically speaking, the f4 aperture isnt really a major hurdle on a modern sensor like yours. You can easily bump your ISO to compensate for dark shrines and Tokyo alleys. Plus, the weather sealing gives you peace of mind if it rains. No complaints at all. Practicality matters tho. Spending your last $2300 on glass is risky when that body needs power. Id put the extra cash toward several Canon LP-E6P Rechargeable Lithium-Ion Battery spares. The R5 II drains them fast... and a dead camera is useless regardless of how sharp the lens is. It just works well for a conservative setup.

Jumping in here because honestly I had some issues with the Canon RF 24-70mm f/2.8L IS USM when I traveled last year. It is so heavy and by day three my shoulder was basically dead. Unfortunately the image quality difference isnt as big as you might think for the extra grand you would be spending.

• The Canon RF 24-105mm f/4L IS USM is much better for walking around all day but that f/4 is definitely disappointing when you hit those dark temple interiors.
• I tried the Canon RF 24-240mm f/4-6.3 IS USM and it really was not as good as expected... the distortion is pretty rough without heavy digital correction and it feels a bit cheap on an R5 body. If youre worried about the low light just grab the 24-105 and a tiny Canon RF 50mm f/1.8 STM for the night stuff. Itll save your back and your wallet. Youll have a blast in Japan anyway!

> I'm worried about the f/4 inside shrines and at night in Tokyo. The 8.5 stops of CIPA rated coordinated stabilization makes the Canon RF 24-105mm f/4L IS USM a total beast. I'm satisfied with f/4 indoors; it works well since that reach's basically essential for Japan.