Pilot Petit 3 fun, pocket mini size Fude pen, also known as brush pen comes with transparent pen barrel and cap. The color clip on the cap indicated the matching ink color for the brush pen. This pen fitted with the clear transparent ink feeder, which allow you to see the fast ink flow to the brush tip. 

Once the ink cartridge finishes, you can easily buy the replacement ink cartridge for replacement. Each container tube comes with 3pcs spare ink cartridges.

Ink sketch sample video link :- https://youtu.be/VNvWXcInY9s