All the stationery in my shop is drawn from my own holster. Sharing my illustration toolbox with you, these items are my personal favourites, go-tos for myriad illustration and lettering jobs.
 
This carbon ink is a pigmented ink, permanent and water-resistent when dry, but it can be worked into with water while still wet or freshly applied for washes and greys. Fits the Platiunum Golden Sakura Brush Pen. Price is per cartridge, since you may not need a whole box.
 
Low-key warning: This ink does have the potential to damage pens if not used according to the instructions - it can clog fountain pen feeds if left too long in the pen due to its very fine carbon particles, so only use in a pen that's in daily use. In your brush pen, it will be fine (make sure the lid's back on when you're finished!)
 
Extra low-key warning: Platinum cartridges only fit Platinum pens.