I'll also be giving reasons for your pokemon as well as a few things about them.
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Sceptile:
This was your Starter.

He has been with you since day 1 and you've been through a lot together.

Like Ash's Pikachu he stays out of his ball, but that's more of you choosing not to return him rather than him disliking the pokeball.

You will return him to his pokeball when necessary like to recover a bit.

He is a reliable partner and your best friend, the both of you are inseparable.

Gardevoir:
A pokemon you actually saved from a trainer who did not want his Ralts believing it to be weak.

You took her off his hands and actually treated it with love and care.

As a result she grew to a rather strong Gardevoir who would risk her life for you.

The reason she has that outfit was because she pretty much begged you to buy it cause she thought it was cute.

Like most Gardevoirs she'll risk her life to protect you especially after what you did for her.

Ampharos:
You helped heal a wound of it as a cute little Mareep and while you didn't catch it then, it was so greatful it followed you home and refused to leave because it wanted you to catch it.

So you did.

As an Ampharos that glowing tail is useful for sending signals at night by flashing it on and off or just a simple flashlight through a dark cave.

Arcanine (Quick question, do you know anyone who Dislikes Arcanine? I don't, I think it's impossible to hate Arcanine):
This was your father's Pokemon, he didn't take it on his last job for some reason and so you brought it along with you to give it back to him when you find him...if you find him.

He is loyal as an Arcanine should be and a good ride Pokemon.

Lycanroc (Dusk):
An excellent pokemon for traversing mountains.

It was the leader of a pack of Lycanroc and after saving it's pack from a rock slide it wanted to battle your Sceptile.

After defeating it, it left another Lycanroc in charge and decided to join you becoming your pokemon.

Excadrill:
Imagine your stuck in a cave during a rescue.

Your Excadrill can dig a tunnel underground without causing a cave-in and get you out.

You found this Pokemon as a Drillbur trying to steal your food at night, you gave it some food and captured it.

Hisuian Braviary:
Now this was an exciting find for you.

This is most likely the last Hisuian Braviary alive and you have it.

You found it at a snowy peak after it saved you from an avalanche.

Since it was the last if it's kind it had nothing better to do than be caught by you.

If it did stay uncaptured then greedy Poachers may have been more likely to find it.

Solgaleo:
Okay, I'll be honest I put Solgaleo here cause Kyoya had a lion-themed Beyblade and Solgaleo was my only option.

I didn't want Pyroar cause Pyroar's pretty lame, Arcanine is more dog and tiger than lion and Luxray is a Lynx not a lion.

Besides you need a super strong Pokemon at some point so you'll only get Solgaleo WAAAAAY LATER in the story.

Will add more later:

Seeing this just makes me smile and hopefully it'll make a few others smile too.