Japan is gonna be awesome but honestly gear shopping is a total nightmare. I learned the hard way that some of the popular cheap options just arent as good as expected and feel really flimsy. I originally bought the K&F Concept 64 inch Aluminum Travel Tripod but unfortunately the leg locks felt super loose after just a few uses. I was constantly worried my camera would tip over in the wind. I eventually switched to the Manfrotto Compact Light Aluminum Tripod and it feels way safer for a beginner even tho it costs a bit more. For bags, I had issues with a cheap generic sling that had basically zero padding. Not great. The Lowepro Truckee BP 150 Camera Backpack is a much more reliable choice.

• Manfrotto Tripod: Very light for walking, but the build quality is actually trustworthy.
• Lowepro Truckee: Fits the a6400 and extra batteries perfectly while keeping them protected. Staying under $200 is tough but dont risk your new camera with junk gear!

Late to the party but I've done the Japan trek three times now. Honestly, the biggest mistake people make is thinking they need a full-sized rig. My first trip to Osaka, I carried a massive setup and my back was trashed by day four. For an a6400, you really don't need heavy-duty stuff. I eventually shifted to a minimalist approach because you're gonna be walking way more than you think. Here is what I'd grab for that $200 limit:

• Sirui Traveller 5A Aluminum Tripod with Ball Head is a solid middle ground. It folds down to about 13 inches so it fits inside most daypacks.
• Tenba Skyline 13 Shoulder Bag works well if you want quick access. It is pretty discreet and doesnt scream expensive camera inside.
• SmallRig Tabletop Tripod BUT2429 for when you really dont want to carry a full tripod. The Sirui is about 90 bucks and the Tenba is around 60. Both are decent options that wont break your budget or your back. Just make sure your bag has a rain cover... it rains a lot more than you'd expect in Tokyo. Tbh, I'd skip the heavy backpacks altogether for Japan.

Saw this earlier but just getting back to you. Japan has super tight spaces so be careful with big gear. I once brought a massive backpack to Kyoto and hit everyone on the subway... it was a nightmare. Stick to smaller items.

• Joby GorillaPod 3K Kit with Ball Head
• Peak Design Everyday Sling 3L V2 The Joby is great but watch out for wind on high ledges. The sling fits the a6400 perfectly without being bulky.