I think that's missing the point. The only way people can still try to make the whole Liko is Ash's daughter theory work is by making huge stretches. Yes, kids can be adopted even when their biological parents are still alive. This is not uncommon. However, in order for that to apply to this theory, that would mean that Ash and/or his partner are deemed too dangerous or irresponsible to take care of their child, something that would not make any sense with both Ash's personality or the more light hearted tone of the anime and franchise as a whole in mind. I don't think that they're going to introduce something like child care services within the anime's universe, so using something like that to explain that Liko could be adopted while still being Ash's daughter would be pretty nonsensical.

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