Magic because when these were first created, in the early 60s, felt tip was brand new technology. As for gel pens and rollerballs, felt tip pens are yet another pen technology contribution from the Japanese.  

This point makes for agreeable permanent marking. It contains a surprising amount of ink and, if the cap is suitably replaced after use, it can fill whole pages. Glass body make for agreeable handling.

Black ink

8.2 x 2.6 x 2.6cm

Presented in a printed cardboard box
8.7 x 3 x 2.8cm