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Need some important additional context here: At what point is/was the character replaced?
Are we talking about a mid-game replacement (say, the tutorial character gets replaced after plot events cause the original one to be unavailable), a replacement between installments in a series, a character being replaced in the course of an open beta as part of the usual tinkering, a character being removed and replaced in response to Unfortunate Implications only realized after release...?
Radically changes what trope(s) appl(y/ies) to the situation.
Edited by Scorpion451

A single or pair of character(s) that were originally present in a video game were later replaced by a different character(s).
The specific example I'm thinking of is a tutorial character who showed off how a game mechanic worked then was later replaced by a completely different character who still preformed the same function. Any mention of the previous character was also replaced.