Name: Ryella Praesidio (pronounced ree-ella pray-see-dee-oh)
Nickname: Ella (only called that by her brother)

Current Age: 20

Place of Birth: Tenebrae

Occupation: Guardian to Lunafreya

Appearance: Has straight, warm brown hair that comes down to her elbows with her bangs parted in the middle. Her eyes are solid green. Has freckles on her nose and cheeks. (Basically like in this picture)

Magic: Can transform into a dragon, but doing so consumes a lot of magic energy. Her own unique form of magic allows her to absorb magic energy (from elemental deposits, for example) and use whichever element absorbed. Eye color changes depending on the current element.

Dragon Form: Covered in white fur with a strip of brownish black along her spine and is roughly the size of a quetzalcoatl, which makes her smaller than her brother.
(In this image, except her eyes are the same green color)

(Here's also a size comparison to show you how big she is as a dragon compared to a person. Sorry for the poor quality, I took a picture of the bestiary image in-game with my phone)

Other Notable Facts: Enjoys playing the harp and singing in her free time. Loves to bake sweets. Can draw fairly well but rarely ever does.

I'm going to go ahead and give you info on her brother as well. And in case you're wondering, I don't give info on their personalities so you can discover them for yourselves through the story.

Name: Reynard Praesidio
Nickname: Rey

Current Age: 27

Place of Birth: Tenebrae

Occupation: Guardian to Lunafreya

Appearance: Has a light shade of black hair slicked back out of his face. Eye color is a mixture of blue and green.
(In this image)

Magic: Like Ryella, he can transform into a dragon. His unique magic allows him to control water.

Dragon Form: Roughly the size of a behemoth
(hard to describe so I'll just give you the image)

(Another size comparison to give you an idea)

Other Notable Facts: Likes to play piano in his spare time. Loves Lunafreya. Keeps his father's necklace on him or in his room (it's basically a family heirloom).
(This is the necklace)

And finally, here's some need-to-know detailed info on Guardians in general.

Every Guardian has heightened senses and is born with an elemental ability that their dragon form is designed for, but they can use it even in human form. While the Guardians can transform, it's not something they can always do at will. Transforming takes a lot of magic energy, especially if they aren't linked to someone. When a Guardian comes of age (at 13 years old) they normally form a magical bond to someone they wish to protect that allows them to share magic energy (if the person can use some form of magic). This allows Guardians of the Oracle or king of Lucis to borrow their energy to transform and use their magic. Being linked also allows strong feelings and emotions to be shared between them, for example, if one is brimming with joy or fear, the other will feel it too. And while a person such as an Oracle can form bonds with multiple Guardians, a Guardian can only be linked to a single person at a time.

Okay, I think that's everything. I know shapeshifting characters are highly overused, but I made the Guardians as realistic as possible and quite like this idea myself. And if you still have any questions about the Guardians or there is something you don't understand, feel free to ask me in the comments and I'll be happy to clear up any confusion.