Not much is known about the pens aside from the fact that there are at least two pens which both serve as a key to the underground shelter. The oldest and first pen was left behind at a different plantation then the Grace Field House, possibly by William Minerva.
The pen has at least 5 known functions:
- Location: When the middle of the pen is opened, it projects a virtual navigation map for the orphans to find their way in and out the Grace Field House. It also shows their location outside the orphanage.
- A key: The pen is the only known key to enter the secret Shelter B06-32 underground. It also is the only known key to enter Minerva's door in Goldy Pond.
- Codes: The pen contains multiple unknown codes and messages.
- Writing: The pen cannot be used to write with.
- Pen Cap: Found in the Golden Lake, the cap gives information about Demons and the Demon World.
- 00-00 is where the Grace Field House is located.
- A08-63 is where Goldy Pond is located as well as the Goldy Pond Resistance. Inside, a windmill is a passage leading to a door that can only be opened with the pen.
- B00-15 is the place where the children ran off to after they escaped from the underground demon trap.
- B01-14 is the location where the children fell into an underground demon trap.
- B04-21 is the number shown in the underground tunnel that leads from the demon forest to a secret shelter.
- ↑ The Promised Neverland Manga: Chapter 38, Page 18
- ↑ The Promised Neverland Manga: Chapter 73, Page 8
- ↑ The Promised Neverland Manga: Chapter 70, Page 16
- ↑ The Promised Neverland Manga: Chapter 41, Page 11
- ↑ The Promised Neverland Manga: Chapter 38, Page 19
- ↑ The Promised Neverland Manga: Chapter 49, Page 4
- ↑ The Promised Neverland Manga: Chapter 51, Page 20