>>56563735This has to do with the partner using either boku, oira (male) or watashi (female) pronouns in Japanese. It's basically 3 different personality types, although it's not as apparent in English.
This is all I can think of for Explorers, and I believe RT is the same for the ones in both games. There may be some mistakes:
>oiraSquirtle, Totodile, Meowth, Chimchar, Munchlax
>watashiChikorita, Torchic, Vulpix, Eevee
>bokuEveryone else
I believe Gates and Super cut this down to just boku and watashi, but by this point localizers didn't bother translating both sets and just took out the partner's gender select. (the US version of Super did keep it) Not sure how RTDX handled it.
In at least Explorers the hero actually has 2 different sets of dialogue as well, but in English it's only utilized in a grand total of 2 lines. Time/Darkness uses it a little more for how other characters refer to you, changing between he/she. (Sky seems to just refer to the hero by name)
In Spanish this is widely used, see image related.