Fulcrum VS Klein

dude I really think you should consider a sideways-mounted 5-way switch for the thumbs like I did on the fulcrum. I think it would work really well on this form factor

You may be interested by the 40-key version of the Fulcrum

It's tough to use more than 2 or 3 regular thumb keys. Check out the Fulcrum for max ergo thumb functionality

I use 20 keys as my daily driver and it’s been a dream come true. My RSI disappeared and as a bonus I type faster than I did before on regular keyboard.

Fulcrum allows you to use one of the thumb joysticks as a mouse, though i wouldn't recommend it as a full mouse replacement

Although, I guess you could also go with your idea with using one hand for the vowel and one for the consonant and use just two 5way switches. There is actually a DIY keyboard with two 5way switches: https://github.com/dschil138/Fulcrum I think it would work well for kana input.

I think you would really like the fulcrum

I doubt this will be what you are looking for but I did the same thing with the keylogger and had the same realization, which heavily informed my keymap and hardware design on the Fulcrum. Full keymap is at the bottom of the readme page. Also if you go to my profile I have a pinned repo on key press stats that you may find interesting.

Fulcrum would be either your dream keyboard or your nightmare keyboard. Not sure which

I humbly suggest the 40-key version of the Fulcrum, which will give your thumbs a multitude of ergonomic options

If you can afford losing pinky column, Klein is almost perfect: https://github.com/snsten/Klein

Klein

Or you could also checkout Klein Klein

All of the files are on this github. You can read about the design process on hackster. The PCB and assembly is sponsered by Seeed Fusion PCBA through this contest.

The firmware is available here and rest of the files are on this repo.