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>canonically form deep emotional bonds with their trainers
>can detect the mood/emphatic state of other sapient beings
>the connection makes them share their emotions/feelings
I know we've already been here, but they're basically overprotective, caring guardians that will feel happy/depressed/etc whenever their trainers are, and if they want, this connection can go both ways to facilitate mutual understanding.
Just imagine your average kid without a pokedex(protag privilige) going on their own trainer's adventure and catching a female Ralts like any normal pokemon, completely unaware about the unique traits of the line. Some time pass and now the young boy is entering puberty and right at that age when you start looking at girls in a different way, and the Ralts is now a fully grown Gardevoir.
Imagine the first time Gardevoir feels how her beloved trainer is being bashful around girls, at first being confused and thinking something bad must've happened with those girls, but quickly realizing what's actually going on. Imagine all those times she feels him masturbating, and is unable to not share his horny moods due to their bond, but she keeps silent about it because she knows it would be very embarrassing for him, and instead chooses to endure it every night.
The thought of Gardevoir being a mature, humanoid female that practically acts like a caring big sister would eventually cross the pent-up mind of the young man at least once, specially when the line is notorious for adoring their trainers. He would quickly discard the notion, embarrassed at himself... but it will be too late, she'd had already sensed it.
All those nights camping in the wild alone with his team... alone with his Gardevoir...
Like seriously guys, realistically speaking, I think adolescent trainers loosing their v-card to a fucking Gardevoir would be a relatively common ocurrence, and pretty much one of those taboos no one is comfortable talking about and everyone just prefers to ignore.