See, there's the normal people, known as Drivers. These come in a wide variety, from the human-looking Ardainians and Leftherians, to the cat-people of Gormott, to the Nopon of Argentum, to the dark-elf-looking Indoline.
All Blades come from these small rocks called Core Crystals, and Blades can come in a wide variety of shapes - from humanoid like Pyra, Brighid and Pandoria, to animals like Dromarch and Finch, to beasts like Wulfric, to... pretty much whatever, like Boreas.
In order to gain a Blade, a Driver must resonate with a Core Crystal and Awaken the Blade. Before this, the Blade has no form or memories. If the Driver has enough Aptitude, they can Awaken a Blade - several, actually, but Jay only has one. Though... he will later gain a second in Chapter 10 of Astrid - Alrest Endangered; Puipui doesn't count since he's a Nopon and not a Blade despite functioning like a Blade in battle.
So in a way, Drivers summon Blades to be their partners and servants.
Jay's the Driver, Penny's the Blade.
Godjacob: I can definitely see the connection between that and the use of Servants in the Fate series, even if really it is more of a mutual partnership rather than the people being human weapons (Theory I know that Jay wouldn't act that way.) I want them to interact.
Heh, you're not wrong. One of the main conflicts of the big villains in the main game is that they're all Blades with a vendetta against humanity, and the heroes only pull through because of the bonds between their Drivers and Blades.
You're right about Jay not acting that way - he considers Penny almost like a sister. If you want to learn about Jay and Penny, actually, as well as get a basic idea of the world of Xenoblade 2, check out my written work series Astrid - Alrest Endangered; it's where they're from. Even though Jay has only shown up as an enemy in Chapter 2 - his chapter is Chapter 3.
Another thing about Blades, actually, is that when their Driver dies they return to their Core Crystal. They can be reawakened, but they lose all memory of their past life and past Driver. Some Blades, like Brighid and Jin, managed to avoid this by writing journals - though for most Blades, they never find their journals again. Brighid's is a royal treasure, while Jin came across his through pure luck.