Futari wa Pretty Cure: Splash Star is not a sequel to this anime. It uses the same basic themes, but with different characters in a different setting. This relation is covered by an "other" link between Futari wa Precure and Futari wa Pretty Cure: Splash Star; there is no relation to Max Heart in particular, so the relation should just be removed.
Also, the image actually corresponds to Eiga Futari wa Pretty Cure Max Heart.
[EDIT][ANIME] Futari wa Precure Max Heart - relation, image
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