Kuretake Maki-e Brush Fountain Pen

This is technically a fountain pen, using Platinum's proprietary cartridge/converter, inner slip cap, and designed to work with fountain pen inks. Instead of a metal nib, you get a weasel hair brush tip for calligraphy or painting.

The screen-printed maki-e body is pretty, too.

I don't have the skill for it but here's a review from Reddit: "I would say that the pen acts like the nicest fine tipped paintbrush I have ever owned, and it feels almost like watercolor painting without having to reload the brush. The brush itself is fairly substantial and can make decently thick lines but it can also make very fine lines if you have the control for it."