What is the longest a character has taken to be added to a game?

Recently a couple of characters got added to Blue Archive after a long period of waiting, but those two are probably nothing compared to other gachas.

Azur Lane for example has Tone who has been in the data of the game since July 2017 and is not just that tho, she has been around for so long without being released that she even got a redesign but still has yet to be released. To add something even more to this, Chikuma is a ship from the same time Tone was added, got a redesign too but she did get released in 2021. So yeah, at this point it almost feels like the devs will never release Tone specifically.

Is there any other character that has had this happened or possibly gone even longer than her without a release?