The 'Felt-Tip Pen' is a gameplay related Item found in Yeondu High School. It is used for saving the game in White Day and (initially) in the remake.
It was later patched at the end of 2015 so that it was no longer required when saving in the Remake version.
however, it's new purpose is to retry upon death in Hell Mode / King Real Mode.
And in the PC/PS4 remake ver, it is used the same as the original ver.
In the Original game, there is a limited amount of pens you can collect and use. With these you can save the game in the men's bathroom, by using the pen on a notepad that is hanged on the wall.
Originally, the usage of the pens was the same as the original game but after the 2015/11/25 patch, Save can now be done freely for an unlimited amount of times. Now, there is no need for pens to save anymore. The pen's new usage is an opportunity to retry, after a game-over in Hell Mode (Wang Real mode).
- It is an equivalent to the Ink Ribbons found in earlier Resident Evil / Biohazard titles, the series in which Sonnori were inspired by and by it's success, to create White Day.