When I make haiga, I use this brush quite often. The brush is made by Pentel stationary company in Japan, and comes with various sizes and colors (grey and red). The ink is supplied by a cartridge(like fountainpen). I posted the link to the manufacturer in comments. The site is in Japanese, though
The brush is usually used to write calligraphy, kanji and all, but in my case, to do ink drawing. It has very fine and elastic hair, so as in the photo, I can draw lines of various types and texture. Depending on the mood of the haiku, I use different lines, and this brush makes the selection possible.