Art Brush: 
The Pentel Art Brush Pens are water based and brightly colored ink flows easily, dries quickly, and produces transparent watercolor effects. Ink filled nylon brush tip is ideal for painting and sketching on location. It's wonderful for writing, illustrating, and drawing. 
To create color gradations, touch brush tips of different colors together. Or to create blurred or lightened colors, touch the tips to water before drawing. 

How to use:
Twist the cartridge part opposite direction, then take off red ring and close.