Ralts/Kirlia/Gardevior/Gallade as nature modifier? Can anyone confirm?

Question

So I play many Pokemon and Gardevior is my favorite Pokemon and so I always make it the main Pokemon and whenever I see or catch Pokemon when Gardevior is my main, the Pokemon always have the same nature with my Gardevior (my Gardevior is Modest natured) and when I tried to take Gardevior from main position, the Pokemon natures become random again.

And so I also catch Adamant Ralts for Gallade and I also make Him in the main position and it also works, all Pokemon I see and catch becomes Adamant.

I dont know if its secret features or not but it works every Pokemon I play with ralts.

Comments

Not a full answer, but https://bulbapedia.bulbagarden.net/wiki/Synchronize_(Ability)

Answer 1

Generations III-V
From Pokémon Emerald onward, if a Pokémon with Synchronize is in the first slot in the party (even if fainted) when a wild Pokémon is encountered, there is a 50% chance that the game will force it to have the same Nature as the Pokémon in the first slot. (Otherwise, the Nature is chosen at random, so the Pokémon still has a 1 in 25 chance of having the same Nature as the lead Pokémon.) This does not apply to roaming Pokémon, Pokémon in the Pokéwalker, or Pokémon in the Entree Forest. In Emerald, it also does not apply to stationary Pokémon (such as Regirock or Rayquaza).

Generation VI
From Pokémon Omega Ruby and Alpha Sapphire onward, if a Pokémon with Synchronize is leading the party, gift Pokémon (except Pokémon obtained via Mystery Gift and Eggs) that are in the No Eggs Discovered Egg Group will always have the same Nature as the Pokémon with this Ability.

Generation VII
In Pokémon Ultra Sun and Ultra Moon only, if a Pokémon with Synchronize is leading the party, gift Pokémon (except Pokémon obtained via Mystery Gift and Eggs) will always have the same Nature as the Pokémon with this Ability regardless of Egg Group.

Generation VIII
In Pokémon Sword and Shield, if a Pokémon with Synchronize is leading the party, wild Pokémon are now guaranteed to have the same Nature as the leading Pokémon (ignoring any Mints). Pokémon encountered in Max Raid Battles or obtained as gift Pokémon are not affected by Synchronize.

In Pokémon Brilliant Diamond and Shining Pearl, entering a Pokémon Hideaway with a lead Pokémon with Synchronize causes all wild Pokémon inside to have the same Nature as the leader.

Generation IX
In Pokémon Scarlet and Violet, Synchronize appears to have no effect on the Nature of wild Pokémon.

Synchronize (Bulbapedia)

It's very likely that all these Ralts you've caught have had Synchronize. This is not exclusive to this evolutionary line -- as stated, this works with every Pokemon with Synchronize (except in Gen IX, where none of them work).