Brush Pens were originally used in East Asian calligraphy as an analogue to fountain pen. The tip of a brush pen mimics a traditional brush used for painting and makes it a very unique tool for modern calligraphy and art. Fudapens (which is just another word for brush pens) are also very popular among comic book artist who prefers them over the traditional way of painting. The first company that created a brush pen was Kuretake from Japan. They've launched their first brush pens in 1973.
If you plan to learn brush lettering, Tombow Fudenosuke brush pens are the number one. They have a smaller brush which is easier to control for newbies☺