Most of these canon info links contain SPOILERS.. though the game's been out over a decade, peeps. Like the disclaimer says, this version of Aerith is canon compliant for Final Fantasy VII and Advent Children and ignores most of the retconning that took place in Crisis Core and Before Crisis. We're also kind of ignoring Dirge of Cerberus because by all reports that game sucked, and Aerith didn't have much of anything to do with it anyway. But the full info's here anyway just so y'all can have it.
Final Fantasy Wiki Entry
Official Square Profile
Name Aerith Gainsborough (occasionally answers to Aerith Gast)
Birthdate February 7
Blood Type O
Age 22 (or 24.. do people age when they're mostly dead?)
Race/Species Half Cetra (mother's side), Half Human (father's side)
Aerith is strongly empathic and capable of healing people (and herself) without the intervention of magic or technology. She is also immune to most poisons, drugs, and toxins though she cannot use this ability on others. As a Cetra, part of her birthright is being able to hear the voice of the planet, which out in the multiverse functions very similarly to a Force sensitivity which functionally gives her a touch of precognition/sense of a person or object's past and clairvoyance (basically, she makes a great mcguffin). Aerith is not telepathic, though she can occasionally detect flashes of memories or sensory information accompanying very strong emotion if she is in skin contact with a person who is going through some kind of deep emotional whatever.
Naturally, what Aerith can pick up will depend largely on what muns are willing to give her. But count on her being able to sense emotions fairly predictably even if a pup is attempting to repress or hide them-- she is generally too polite to make a big deal of this, though it sometimes makes for weird conversations if she responds to the emotional cues she's picking up. Even without prompting from her otherworldly senses, Aerith is a keen observer and does tend to notice and interpret small details-- she was the first to figure out about Cloud and Zack, for instance.
In the past, Aerith has been able to call on the Lifestream to essentially perform miracles, such as creating the healing rain that cured geostigma on her world or summoning the Lifestream to repel Meteor. Since Aerith has left her planet of origin and left the Lifestream, she cannot perform such miraculous feats without entering a similar near-death state and merging with the local Lifestream. Since this has a chance of killing her again, she is not likely to do this unless whole worlds are in peril.
Aerith has a deep affinity for magic and in addition to her healing powers is a master at the use of materia. She habitually carries the White Materia (capable of casting Holy) in a materia slot in her hair ribbon as well as the following mastered materia in a Minerva Band (which protects her from fire/cold/gravity/holy type attacks): fire, contain, heal, revive, restore-all. While Aerith can sometimes be found with the Princess Guard, she does not carry materia in it. She has ALL her limit breaks, including Great Gospel, and in Final Fantasy VII terms would be somewhere in the mid-60s as far as her level. (So, tough, magically powerful, and able to join the party on the final boss fight.)
Speaking of the Princess Guard, Aerith does know stick-fu well enough to reasonably defend herself, though she's no match for an expert in a straight-up physical matchup-- most of her self-defense knowledge is situation recognition and the art of running away when she's without access to magic. Hence why she's always carrying materia. Though why you'd want to fight her heaven knows...
Aerith is the only child of Ifalna, a Cetra, and Dr. Gast, a scientist working for Shinra Electric Power Company. She was born in Icicle Inn not long after Gast fled Shinra with Ifalna. When Aerith was only a few months old, Professor Hojo found them, murdered her father, and kidnapped both Aerith and her mother.
Aerith was a captive of Hojo's for several years, until her mother escaped with the help of the Turks (strictly under the table). What she suffered at Hojo's hands can only be conjectured, but let's just say that Aerith learned about her ability to clear poison from her system the hard way. Ifalna did not survive the escape attempt, and with her dying breath left Aerith in the charge of Elmyra Gainsborough. The Turks were dispatched to bring her back in, but instead they aided Aerith and Elmyra in hiding from Shinra as part of their longstanding quiet feud with the Science Department. Ironically enough, Reno and Elena were some of Aerith's closest friends growing up.
Aerith grew up in the Sector Five slums, living a contented life on her adopted mother's meager salary and the money she was able to make selling flowers. She grew to be friends with Zack Fair, even to the point of a couple dates, before he mysteriously disappeared during a mission to Nibelhiem. While she never met Cloud and Sephiroth directly, she heard a lot about them second-hand from Zack and was their secret supplier of baked goods.
She finally got to meet Cloud five years later, only Cloud was convinced he was Zack, and she helped AVALANCHE discover a plot by Shinra to collapse the Sector Seven plate by helping Cloud infiltrate Don Corneo's operation in Sector Six. She was finally kidnapped by Turks while AVALANCHE was attempting to foil Shinra's plot to drop the plate, and rescued by AVALANCHE when Cloud later led an infiltration of Shinra Tower. When Sephiroth appeared and went on a murderous rampage through Shinra Tower, Aerith joined AVALANCHE in their mission to find out what was going on and stop Sephiroth's madness.
After Sephiroth was able to recover the Black Materia from the ruins of the Temple of Ancients, Aerith left AVALANCHE and headed to the Forgotten Capital on the north continent to attempt to summon Holy using the White Materia. She was able to complete the summoning, but Sephiroth appeared and stabbed her, ending her physical existence for the time being.
Aerith lent her aid to AVALANCHE from the Lifestream, eventually summoning it to defend the planet from Meteor when Holy failed to stop it. She spent the next couple years trying to root Jenova out of the Lifestream and counter the geostigma plague that was sweeping the world in addition to catching up on the whole "knowledge of the Ancients" thing that was her birthright as the last Cetra. Two years after Meteor, she once again helped AVALANCHE to stop Jenova and Sephiroth, creating a healing rain that cured geostigma and aiding Cloud to defeat Sephiroth a second time (which might have been a super-powered manifestation of her Great Gospel limit break, sans goofy angel animations).
With Jenova completely gone from the planet, Zack's spirit was able to continue on to the Promised Land, along with all the others who bore Jenova's cells. Aerith... ended up in the multiverse. At least she has a body again now.
What you can do with Aerith: Everyday sort of discussion interaction, getting requests for food/candy/flowers/plants/baked goods filled, and magical healing are all awesome. I would prefer PMs to work out general goals if Aerith is going to be involved in fighting, just so that we're both clear on what's going to happen there. (I'm really pretty flexible when it comes to RPing combat, I just don't want any misunderstandings or for the log to drag on forever.) DEFINITELY PM me for situations that might get Aerith killed (again) or severely damaged... or if you want to use her Super McGuffin Powers from merging with the Lifestream, since that's pretty game-breaky. (I prefer not to do any of those things listed on a whim, hence why I'd prefer a PM.) As for her Normal McGuffin Powers of being able to pick up things and/or hear the voice of the planet and/or hear the words of the recently dead, hey feel free. We don't mind using her to help advance your plots. Just give me an idea of what she's supposed to be picking up in order to react/relay it to your pup.
What Aerith can do with you: Aerith will happily cook and/or take care of people, garden, use magical healing, and talk/listen with your characters. She makes a great McGuffin if you're looking to resolve any sort of mind-whammy, secret past, need for emotional closure sort of plot since her skillset leans in that direction. Aerith is also available for mysterious prophecy if your plot requires it, but give me a heads-up what you need your pups to learn since I suck at being a fortune cookie off the bat. If fighting is what you're after, Aerith can mess you up with magic pretty good. If it's a ginourmous, world-scale threat, she can do the Lifestream merge trick, though that might kill her for good. (I'm planning on rolling dice, at a penalty for each time she's used it, on whether or not she can get back to her body.) Aside from magic and knowing things, though, Aerith's skillset is mostly domestic.