Laventon is probably a unique character, but you could argue he's an ancestor of Professor Rowan due to both being the Professor of Sinnoh. Cheren, Hop, or Leon are other possibilities.
Iscan seems like another unique character, but you could say he's the ancestor of Nessa due to the similair hair and skin color, as well as the affiliation with Water types.
A little bit of Trivia about Arezu: The name is derived from the Greek God of War, Ares, whose Roman counterpart is Mars.
This pretty clearly points towards Arezu being the ancestor of Mars.
Of course, this is all just speculation and we likely will never get a definite answer.
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