Imagine Gardevior but a tomboy
Backstory
Originally, there were meant to be a choice between three different starter Pokemon: Chikorita, Cyndaquil, and Totodile. However, through the fault of no one, this did not happen.
The Cyndaquil became too attached to the lab assistant who raised it- too attached to be given away! So, they needed a replacement.
Carter, the lab assistant, was from Hoenn originally. One of his contacts had recently hatched a baby Ralts, and everyone agreed it would be a great choice of starter Pokemon... even if they were a little difficult to raise at first. The Ralts was given to Professor Elm's lab to take care of until a trainer for it could be found.
How Gold obtained it
Ralts are three things: Quiet, timid, and adorable. They are small, their body creates the impression of a nightgown they have to waddle around in, and the red horns on it looked closer to pink.
They are also rather rare in Johto.
Gold, an enjoyer of cute things and unintimidated by the threat of a challenge, picked her as his starter. He named her "Silklay" because of the texture of her hair.
Although Gold was completely up for the challenge of raising a small baby Pokemon into finally a very strong one, even if it would take some time, the challenge he was initially faced with was more than he was expecting. To go out into the wilderness, people say you should take a Pokemon with you. The purpose of bringing a Pokemon is that it can defend against any wild Pokemon you may find... and Silklay didn't know any attacking moves.
Carrying the Ralts in his arms, Gold had to run through the forest to get out of dodge. He managed to get to Cherrygrove city, but just barely. This, however, was not the end of their troubles. He recieved a panicked call from Professor Elm, making him run back to town. On his way back, a red haired passerby boy with a Mareep attacked them, and, not knowing how to battle, the Ralts fainting was predictable.
Upset about the unprovoked attack against his defensless baby Pokemon, Gold shoved the boy and grabbed his belongings. The stranger managed to take them back and run off, but not before Gold managed to look at his Trainer ID. He saw his name: Silver.
When Gold managed to get back to Professor Elm's lab, he learned that a Mareep had been stolen. Gold, remembering the Mareep Silver had, quickly connected the dots that the Mareep he used must've been the same one from the lab. He promised to Silklay that if they ever ran into Silver again, they'd be able to beat him.
Congratulations! Silklay has evolved into Kirlia!
After Gold caught Atticus, he became the battling Pokemon of the team. He didn't want to force Silklay into any battles, as he was worried that she was put off by her first experience. He would always carry her around in his arms, but if they were in a trainer battle or going against the gym, he never sent her out and would only use Atticus.
Ralts can read emotions, and could tell how much fun Gold and Atticus were having battling without her. Though she was still shy and unsure of her abilities, she started insisting Atticus teach her how to fight. Atticus is a Dark Type, and as a pure Psychic Type she was naturally scared of the Houndour, but this just helped her push through her fears.
Soon, she learnt the basic attacking move of Confusion. With the ability to fight now, Gold started using her in battles. She soon evolved into Kirlia.
Silklay is a Pokemon that isn't normally found in Johto, so trainers will often comment on her as unique or odd. This is especially so, because while normally Kirlia's hair is long and straight, hers is messy and short.
The reason for this is because Kirlia is an empathetic Pokemon that is more likely to change their appearance to not only match their trainer, but compliment them. Ralts are most commonly given to shy or otherwise antisocial trainers, so tend to have a calmer, soft-spoken, motherly sort of personality. Gold, however, is outgoing and energetic: the opposite of most Ralts trainers. Thus, she's much more tomboyish and seems far different to most members of her species.
Congratulations! Silklay has evolved into Gardevoir!
Silklay's rougher hairstyle carries onto her evolution, matching Gold more closely. In personality she's rather similar to him, and will immitate human behaviors such as clapping.
Of all of Gold's Pokemon she spends the most time outside of her Pokeball. She's often seen walking beside him, and will try to translate what a Pokemon is saying to the best of her ablility. However, she cannot speak human words. Silklay has heard of Psychic Pokemon being able to transmit words through thoughts, and she wishes to one day learn this ablility for herself. Despite not being able to talk, she is determined to express herself in what ways she can. Her hands are not very dextrious, so she struggles to write, but she will often draw pictures on paper.
In some regions, Gardevior is a Psychic/Fairy Type. However, Silklay is a pure Psychic Type. This is because in order for a Pokemon to be Fairy Type it has to be around other Fairy Types. They aren't common in Hoenn, Johto, or Kanto, so she has remained a Psychic Type. If Gold were to travel with her to another region where Fairy Types were abundent, it is possible that she might gain the secondary typing.