So, in Pokémon Sword and Shield we learn that giving your crush an Applin is condiered a romantic gesture, used to express your feelings for the one you like.

This custom is inspired by how the Ancient Greeks used to propose - by throwing an apple at their chosen bride.

Some sources claim that throwing an apple was more of a "love spell" rather than marriage proposal, but regarldess of which version is true (or if both are), in Greek Mythology apples were deeply tied to Aphrodite, the goddess of love and beauty. A Golden Apple is considered one of Aphrodite's main symbols, and she is portrayed holding it in a lot of pieces of ancient art.

Now, another myth in which apples are tied to marriage is the Golden Apple Tree guarded by the seven-headed dragon Ladon. The tree was a wedding gift from Gaia to Hera, the Goddess of Marriage, after she became Zeus's wife.

Ladon, the dragon guarding the Golden Apple Tree is portrayed as a serpent with seven heads - just like Kieran's ace, Hydrapple.

Even Hydrapple's name links it to Greek Mythology, as Hydra is a beast originating from it. Not to mention, shiny Hydrapples are golden, just like both Aphrodite's apple and the Golden Apple Tree from the Garden of Hesperides.