What's some amazing technology they have in Japan that's very normal but as a blow your mind here

Its the small things, not anything massive.

For example, most toilet paper holders in Japan have this floating lid that sits on the toilet paper, which allows you to cleanly rip a sheet off every time, and prevent tearing a corner off.

The suica or iccoca cards (trains and subway cards) can be used to tap to pay near everywhere, including vending machines and such. Quite convienent.

You can pay many of your utility bills, in cash, at most main convienence stores. It allows for more methods of payment outside of everything tracked by credit card.

Many shower rooms ( Japanese bathrooms tend to have a full wet room for bathing) often have an advanced fan system, with a dehumidify option for drying clothes you hang in that room.

Many bathtubs have a water recirculate option, which reheats the same bathwater keeping it warm without needing to refill or add water to the tub.

Ah, one of my favorites is in many bedrooms there is a small square panel on an outside wall, and if you click it it vents to the outside, providing outside fresh air without needing to crack a full window. They often have filters built in as well.

Its becoming more common in the US now, but minisplit AC systems are ubiquitous in Japan. Its nice being able to control each bedroom separately.

I could go on. I lived there for a bit with my wife, in Osaka and in her hometown ( in Nagano).