Name: Shini Gladiolus
Age: 15
Sexuality: He has no clue, I have no clue, Blu is having a day off, we're all clueless!
Gender: Male
Looks: Below
Personality: Sarcastic, Loud, Erratic, Disillusioned, Odd, Probably untrustworthy, Paternal given certain circumstances.
Species: Gifted Human (Part Bone Golem)
Powers: Necromancy, Umbrakinesis, Speed, Soul Absorption (If something dies near him, he can eat it's soul and heal himself, or harvest it and gain it's special traits. Or, on contact with a body, he can 'trace' their soul around his own, letting him temporarily copy what they do within a 1 metre radius of him.)
Weakness: Memories. As in, old things imbued with powerful memories hurt him more.
Likes: Animals, Warm places, Video games.
Backstory: Shini and Cerbera share one, and I shall write it in a separate thingamabob down below.
Weapon: Powers, fists.
Crush: Doesn't have one, as of right now.
Other: His right arm and left leg are constructs made from necromancy. Thin bones as a base, covered in years-old solid shadows and darkness to create new, even more effective limbs. (If you want to know what I mean by more effective, think Rentarō Satomi) Although Shini can't be called overprotective, he also can't be accused of not caring for Cerbera.

Name: Cerbera Gladiolus
Age: 14 and 350 days.
Sexuality: She has no clue, I have no clue, Blu is having a day off, we're all clueless!
Gender: Female
Looks: Also below.
Personality: Cynical, Erratic, Disillusioned, Odd, Issues with trust.
Species: Gifted Human
Powers: Photokinesis, Flight, Healing, Ascension (Able to grow up to twelve wings from her back. For every pair she has, she gets progressively stronger, faster etc etc. She needs to be surrounded by extreme amounts of either light or darkness to start sprouting wings, and loses them after a while.)
Weakness: Wounds dealt to her with Obsidian take longer to heal and can't be healed by her.
Likes: Quiet places, Video games, Stuffed Toys.
Backstory: Shini and Cerbera share one, and it shall be below.
Weapon: Powers, fists.
Crush: Doesn't have one, as of right now.
Other: Has a habit of using Shini as a comfort object; IE if she's scared or confused she'll likely let him deal with the problem, or literally hide behind him until it goes away. Not that he minds, he finds it rather cute/good teasing material. Also, if by some miracle you manage to find it, she has a teddy bear. Touching it WILL get you put on her shit-list.

This is what they look like:

Except Cerbera's hair reaches her shoulders and she wears a light pink t-shirt, a blue jumper and blue jeans. Shini is pretty much spot on.

Also, backstory and a shared weakness between the two of them:
Background: Shini and Cerbera were normal humans living normal lives. Well, then they turned 7. At that point, they were talking together late at night about comic books, when their powers literally surged out from them in a glorious awakening of light and dark. (That occurance has nothing to do with the fact that they both cringe near comic books. Nope, not at all.) When their (normal, highly religious human) parents ran upstairs to see what the commotion was about, they saw a blindingly white angel staring at a demon oozing darkness and shadows.
Blinded by not only the light, but also religious fervour, the father threw various objects at the demon, until various snaps could be heard and the two figures ran out.
Running on adrenaline and fear of their parents, who they couldn't figure out why they attacked them, Shini eventually collapsed from exhaustion and a broken leg and dragged himself to a park bench, the darkness having long since stopped appearing around him. Cerbera followed him and they slept the night away on the bench.
The next day, they started a stereotypical life on the streets. Stealing, cheating, sneaking, fighting, pick pocketing, whatever. Along the way they learnt more specialised stuff, like hacking, cooking, poisons, counterfeiting and their powers. They both and a separate coping mechanism, which ended up altering their personalities. Shini became very Hazama-like (Look up BlazBlue) and started goofing off in an attempt to amuse Cerbera, whilst said sister started to shut herself off and trying to be an constant rock for Shini to rely on.
The last problem to happen to them before they were found by the government was about 3 years after his leg and arm were damaged, (Cerbera only learnt healing on the 4th year.) said limbs fell off, due to gangrene and neglecting their poor state for years.
When that happened, Shini used necromancy to grow a flexible strut of bone out from the stump, then wrapped them in hundreds of micro-layers of darkness and shadows, ending with a single clawed hand and an angular foot.
So, yeah as mentioned, after that, they were found by the government and put in the program. The rest is yet to happen.

One weakness that applies to both of them, although it is mental. They already have a physical one, so it SHOULD be fine. I think. Eh, either way, here it is:
So, who's seen No Game No Life? No? Just me? Okay. Well, the two main characters, NEET siblings Shiro and Sora are near geniuses transferred from earth to a place named Disboard by it's God, Tet. Anyways, my point is, if the two protagonists are separated from each other, they have panic attacks. As in, one of them was put on the other side of a closed door, and by the time we could see either Sora or Shiro, they both had curled into the foetal position, rolling back and forth and calling for each other. The door was opened, and they were immediately up again and running at each other...
What was my point again with this...? Oh, yeah! If Shini and Cerbera are separated, they are fine. However if they go a long period of time without contact with each other, they will start worrying, then they'll get violent, then they'll just roll into a ball. So, long story short, don't separate them for too long. Also, for God sake, don't threaten either of them within earshot of the other.

Done!