A rollerball pen made with Kakimori, a Tokyo stationery shop, for the Hobonichi Techo planner. Kakimori call the design Frost: the polycarbonate body is translucent and finished like frosted glass, so the ink inside shows through as a soft shadow.

It writes like a ballpoint, with a rolling tip, but it is fed with liquid ink from a converter you fill yourself. That means any bottled colour you like, laid down smoothly, with the shading a good ink gives.

Why people love it

• 134 mm long, 14 mm across and about 14 g, so it rides in a planner cover or a pen case all day
• The grip section is long, so your fingers rest well away from the step in the barrel
• The cap screws on rather than pulling off
• The body is Hobonichi's own khaki gray, with the TSUKI no IRO logo pressed in silver
• The frosted wall lets you see how much ink is left, and the pen takes on the colour you fill it with