I have found the Pilot Kakuno (about ¥1000, so inexpensive) - just IMO, - pilot ink is very easy flowing, the nibs are great for my writing style, pull off cap not screw, so much easier and readier to use, easy to clean. I work in the UK health service which is not a good place for stationery lovers.

A well-tuned fountain pen should write with only the weight of the pen, and then it can take time to learn to relax the hand and shoulder.

I can type for longer without pain than I can write with a ballpoint or a pencil, but a fountain pen exceeds them both.

Maybe I just have bad technique. I feel like I can’t relax the hand but have to actively use it. Longer writing is definitely painful.

Relaxing isn't easy by any means, at least for me, it takes a lot of practice.