Disclaimer: I own nothing but the idea.
Ianto Jones had been a fairly unremarkable boy, living in a fairly unremarkable house, in a fairly unremarkable town. He lived with his Tad and Mam and his sister Rhiannon, and on Sundays his Nain and Taid would come round for tea and tell them fantastic stories of monsters and magic. His Mam didn't like it when they told those stories, though, so it was mostly regular stories out of a book.
And then Ianto started seeing the monsters.
His first wesen turned out to be the girl who sat next to him in Maths. When he'd asked her after school if she had scales because of an illness, she'd paled and ran to her parents. The Daemonfeuer family was gone the next day. Family emergency, you understand.
When he'd told his Mam, she'd gotten an awful look on her face, and called Nain and Taid around. Rhiannon and Tad were as confused as Ianto, and while Mam carried a harsh whispered conversation with her parents behind closed doors, Ianto was pestered with whys and whats. Eventually Mam and Nain and Taid came out. Mam and Taid took Rhiannon and Tad in the other room and Nain came over to him and quietly asked Ianto to pack all his things away.
When he asked why, his Nain told him he'd be living with them from now on.
So he'd packed all his things away and put it in Taid's car, and when they drove away with Tad and Rhiannon and Mam watching from the door, Ianto wondered how long he would have to stay away.
His Nain and Taid taught him everything he needed to know about being a Grimm, and then told him sternly that everyone was still learning, and if he didn't want to get himself killed he would study and keep fit for the rest of his life. Ianto passed through secondary school this way, and despite being bookish and quiet, no one ever bullied him because of the one time he'd broken the nose of the thug four years older than him.
When he was fifteen, he was caught shoplifting, and when the police showed up on his Nain's doorstep, she told them thank you and dragged him inside. Ianto was then given a lecture about stealing and how he was sloppy enough to get caught.
When he was eighteen, the police showed up again, this time to tell them about how Ianto's Tad died in a car crash, and his Mam had to be institutionalized because she'd almost killed the other driver, screaming about snakes, and they were very sorry for their loss, but could they please take in the daughter, as she had nowhere else to go?
And suddenly Rhiannon was back in his life, angry with grief, indifferent to her brother who she hadn't seen since he was ten, and most importantly—not a Grimm. She was old enough to get her own place, so Taid gave her some of their not-inconsiderable funds, got her a job interview, found an estate for sale, and sent her on her way.
It was safer for everyone that way.
He tried university in London for a while, and then came back to Cardiff when he'd noticed strange people in suits looking around campus—with guns. He asked around before he left, and a relatively reliable Mellifer told him all he wanted to know about Torchwood.
Shortly after Ianto's twenty-second birthday, Taid passed away. Nain became more withdrawn, and six months later fell ill. She called Ianto to her room, as she'd refused to go to a hospital. She told him she was leaving everything to him, including the city.
"What do you mean, Nain," Ianto asked. "We don't own the city."
Nain smiled. "Perhaps not in the eyes of humans, Ianto. But to all the wesen that reside here, we keep the peace. We keep order, not the royal families."
Ianto frowned. Despite his teachings, not much had been said about the royal families. "Why not?"
"We have an agreement with the wesen here, Ianto. If they don't cause trouble or bring attention here, we protect them from humans and the royal families." Nain coughed, clutching her chest. Ianto quickly filled a glass of water and knelt by her side again.
"What about Torchwood, Nain? Do we have an agreement with them too?" Ianto asked gently.
"No." His Nain looked weaker by the minute. "They do not know of us. The main branch in London does not sit well with me, though perhaps the others are different. In Cardiff, Torchwood is lead by a man called Captain Jack Harkness. Some generations have made a passing mention of him before. At first I thought it was a family name, passed down, but there might be something more. Now," she looked at him seriously. "There are books in your Taid's study that we did not let you read. They are yours now, and they will help you. After you read them, go the place called 'Sanctuary'. It is a wesen recreational meeting place, of sorts. Neutral ground. The owner is a Jagerbar, and he and his family are old allies of ours. I know you will do well, Ianto."
Ianto held her hand and cried silently as Nain's eyes slipped closed. Her chest moved once, twice, three times, and then stilled.
He sat there for a time, and then gathered himself to make arrangements. He was no stranger to death, and knew he should be happy his Nain was allowed to die peacefully, unlike so many other Grimms.
Ianto made the phone call to the mortician and the lawyer, and then opened the door to his Taid's study with reverence. He'd never been allowed in here before, and the fact that it was only possible because of his family's deaths made the occasion bittersweet.
The study was every bit as elegant as the rest of the house, magnificent and yet warm and homey. It reminded Ianto of the studies designed in 1900s movie sets, like Professor Kirk's in the Narnia Chronicles; a true grandfather's study.
The old books that lined the walls were obviously Grimm texts, but most of them Ianto had never seen before. He looked over the nearest shelf and pulled out the first unfamiliar tome. The Life of Cardiff Sewers. Lovely.
Hours later, long after night fell and Ianto lit a fire and candles—he much preferred to read by natural light, and central heating had nothing on a fire's comfort—he sat back in the desk chair and rubbed his eyes. Many books were spread across the room, but the few most important ones were in front of him on the desk. The Cardiff Rift, The Shadow Proclamation-Grimm Treaty, History and Warnings of the Royal Families, and Torchwood and UNIT.
The study seemed to hold mostly Grimm's accounts of alien life on Earth and human's response to it. The treaty between Grimms and the Shadow Proclamation was brokered by the Doctor, and basically said you stay out of our way, and we'll stay out of yours. Of course, this only applied to justice within the SP's jurisdiction, and once they didn't have a foot to stand on, Grimm's got priority.
There were a few books on the royal families, detailing the wars over Cardiff, Wales, and the United Kingdom in general, with the Grimms' victory. There was a diary from the Jerusalem wars as well, but Ianto was a little rusty on his German and Latin. Honestly, he just couldn't be bothered right now.
He heaved himself up with a sigh, glancing at the embers of the fire before blowing out the candles. He'd get some sleep, go to the funeral, work out any legal issues, and then go to the Sanctuary Nain talked about. He might even find out a little more about Torchwood.