You're going to need this: https://en.wikipedia.org/wiki/Ink_eraser

(We called it 'ink killer' in school, you were however not allowed to use it the first few years after switching to ink from pencil.)

addendum: And you can get ballpens with the ink as well.

I highly disliked them, the result always looked off to me. At some point in school, I reverted to just striking through everything.

Yes, and they smell like pee

Erasable blue ink tends to fade away after a few month/years if the paper is left a bit exposed to air or humidity, since the eraser uses a chemical that is also present in the atmosphere. So be careful if you intend to use it.

Whats even more awesome: The ink is not erased, but literally made invisible by manipulating the molecues in the ink "responsible for the color". By reverting this chemical process, the ink can be made visible again!

Invented by Pelikan in weimar germany!