They say write what you know, and I know superheroes.
Mikasa
Mikasa is the powerhouse. Superstrength, flight, the works. It ain't a party til she gets there. She has a very black-and-white outlook: something is either evil or good. She is also quite ruthless with whatever unfortunate soul she catches perpetrating a crime.
Armin
Armin doesn't have any natural powers, but he makes up for it with his intellect. He has dozens of gadgets for everything, including gauntlets that give him artificial superstrength. However, his preferred weapon (if it can be called that) is a forcefield that he may or may not have stolen from an alien race.
Marco
Marco is the human (or, y'know, metahuman) equivalent of a bloodhound. He can subconsciously sense the energy signatures that people and certain objects leave behind, and track them literally anywhere in the world. He also has a pair of wings that enable him to fly as quickly as a jet, and have earned him the nickname 'Angel'. He has to eat almost constantly to make up for the calories he burns while flying.
Jean
Jean is a natural leader- a real Captain America or Cosmic Boy, if we're going to make allusions to DC or Marvel. He channels electricity in the air and from anything electrical nearby, making him quite literally a 'hot head', but really it takes quite a bit for him to lose his 'cool'. Heh. He's just as suited to openly leading a charge as subtly leading from the back. He also has some latent ESP, which may explain some of his leadership abilities.
Eren
Eren is nobody, at least at first. He has no clue that his sister is a crime fighter, or the kind of 'overtime' she puts in at the office. But when Eren's latent metagene kicks in, giving him incredibly increased strength, durability, and speed, it does so with a vengeance. And of course, Eren does what anyone would upon discovering their superpowers- he puts on a cape and goes out to kick some evil ass.
Annie
Annie is a natural telepath, and has been since she was seven years old. Though still a teenager, she is the strongest mental power in the country. She picks up on her comrades' thoughts unconsciously, although she tries to respect their privacy. She has mentally beaten crooks into submission, and more than once a bewildered criminal has found himself the city police station after having an irresistible impulse to 'turn himself in'. She also has some telekinesis.
Reiner
Like many metahumans, Reiner has a secret identity. Unlike many metahumans, he was Brawn before he was Reiner. Reiner was raised in a test facility somewhere in the Central American desert, and for most of his life was referred to either as 'Subject 104' or 'Brawn'. All he wants to do is fit in with the rest of the world, but Annie and Bertl tell him it's not time yet. Just once more, then they can stop. He has amazing strength and stamina, but his sanity isn't as resilient as his body.
Bertolt
Bertolt, like Annie, had psychic gifts. Unlike Annie, his are not natural. Bert's ESP was triggered artificially in a lab, and while he is nothing compared to Annie, Bertolt can be a force to be reckoned with. He knows what they have to do, and while he's not happy about it, he has an unwavering sense of duty.
Christa
Christa is a witch on the run. Since she destroyed the source of her coven's power, her coven- the Reiss clan- want her back, and will do anything to accomplish that goal. Chista has been a faithful practitioner of the 'white' magic- nothing with malevolent energies, nothing that would kill another sentient being- but lately she finds that her aptitude for white magic is waning… as her abilities with black magic increase.
Ymir
Ymir never meant to leave her home planet, Sanyu, and she sure as hell never meant to crash into Earth's magnetic north pole and be flash-frozen for nearly seven hundred years. But something has awoken her after all these centuries, and when she finally awakes, Ymir has questions. Can she blend in with the Earthens? What kept her alive for 700 years, and what woke her up? Does this have anything to do with the fact that as the next in line for the Sanyuki throne? And will she ever be able to return to Sanyu?
Sasha
Sasha is the first of her kind: A Watermaster with extremely powerful control over her opposite Element, Fire. This dual control of opposote Elements has made her a dangerous rival to every other Elemental master. Every Master has Magical servants of their own Element: Earth has Brownies, Water has Rusalkas, etc. But because Sasha has control of Water and Fire, neither Rusalkas nor Dragons will have anything to do with her and both species are determined to destroy this abomination to the natural order.
Connie
Connie has been living on borrowed time for as long as he can remember. Diagnosed with leukemia at age seven, his life has been a series of doctors, chemo, therapists, more chemo, and hospital visits. An experimental cure has left Connie in remission, but it's come with some unusual side effects. Namely, bright blue skin and claws.