No one except the Dragon Clan knows exactly where they came from. Unlike most of historical Johto, the Clan prioritises keeping extensive records regarding their history, including the everyday proceedings of the Clan and the surrounding area. However, these records are highly protected, so no besides record-keepers, the Elder, and individuals with permission from the former are allowed to access them.
Long ago, their community was used as a rest stop for travelers flying between Johto and Sinnoh (no inter-region land routes existed back then). However, the outsiders that wanted to stay were not allowed to take up residence within the clan, so they had to build their own town nearby—this would eventually become Blackthorn. In modern times, commingling between the Dragon Clan and the outside world is much more common, but non-clan members (anyone who hasn’t been born to an existing clan member) still cannot live in the community. Most mixed families will choose to live in Blackthorn or the immediate surrounding area as a result, even though there has recently been pushback against what some believe to be an outdated tradition.
On a similar note, while visitors are welcomed in the community, no non-clan members are allowed to access the Den itself without a special token---a Silver Wing carved out of a Dragon Fang---given out by the Elder or a trusted representative. This is because it houses the dragon egg/hatchling incubation areas, historical records and cultural/religious texts, and the Clan Elder’s living quarters. More importantly, it’s a sacred space dedicated to Lugia, who the clan believes to be the ultimate dragon pokemon.
Roughly a century and a half before GSC/HGSS, the Dragon Clan was forced to integrate into Johto after going through some hardship. It’s legally considered part of Blackthorn and therefore has to follow Blackthorn laws, but otherwise considers itself independent and self-governing.
Additionally, the community is fairly self-sufficient, growing most of its own food and having a generally closed economy that operates mostly through bartering. However, money is still exchanged between the Clan and Blackthorn. Clan members usually buy necessities while Blackthorn residents and tourists often visit to purchase artisanal products, especially jewelry. Dragon Clan jewelry is considered some of the most valuable onm the Sinnoh/Kanto/Johto continent, partly because the Clan is the only group of people who is legally allowed to harvest materials from dragon-type pokemon, and partly because the Clan’s jewelers are some of the best at their craft. The jewelry is even said to exude different properties based on the material used—Dragonair pearls, for example, are said to impart both elegance and power upon the wearer. Silk also used to be popular, though it's now an endangered tradition since the Spinarak populations used for production have largely migrated towards warmer climates.
The community itself is built around the entry lake to the Den, located a couple miles north of Blackthorn. The residential area is built closest to the lake, with businesses and shops found more towards the south of the community. The very outskirts are dedicated to dragon rearing, mostly consisting of pastures and shelters reserved for the pokemon as well as sheds to store necessary resources. The rice fields, which produce the community's main source of food, lay further up the steep slopes of the mountain. More housing is scattered between the community and Blackthorn, where most of the mixed families reside.
Both Blackthorn and the Clan community feature gassho-style architecture. However, while Blackthorn has mostly modernized to resemble Johtonian interiors with features such as sturdier interior walls and full wooden doors, the Clan’s homes are still structured like traditional minka.
The Dragon Clan hierarchy basically works on a system of prestige. The more you contribute to the clan, the more prevalent you are in the community. This doesn’t mean much in terms of actual power, as the only real position of authority is the Dragon Clan Elder, but it does mean you get all the nice benefits that come from being well-respected such. (this might sound weird but the best way I can think to explain it is that it's like raising the most money for your PTA bake sale and getting voted for PTA president in the next election. maybe the school admin gets the last say on what happens in the district, but you still have a ton of sway and people who will listen to you regarding district matters)
Although candidates for the next Clan Elder are traditionally kept within the family, there’s no official rules for the selection process—no birth rights or anything like that—meaning that impressing the current elder is very important if someone is aiming to claim the position next.
Once an elder is chosen, they belong to the entire clan, quite literally. They move away from their family unit to their own special housing from where they are expected to lead the clan with a just, impartial hand. In return, the clan takes care of them—their home is kept tidy and comfortable, their food is prepared and served everyday in a timely manner, and their every possible need is handled by the members of the clan.
Unless the elder assigns a specific task, chores (mostly revolving around clan upkeep and community service) are decided upon collectively by the clan. Everyone except for the youngest of the young and oldest of the old are expected to contribute, as the more hands there are available to help, the more the burden can be shared. Assignments are not permanent, and clan members may reassign work or trabe jobs with each other for the betterment of the community.
Aforementioned public sway comes in handy here, as more esteemed individuals typically delegate themselves the most prestigious jobs (aka whatever gets them closest to the Elder and/or takes the least effort while still making them look good) while everyone else divides the less desirable jobs among themselves. There’s technically nothing stopping anyone from protesting such a system, but making too much of a fuss might mark you as a troublemaker in the community’s eyes.
Unless owned by a specific person or family, most of the dragons of the Dragon Clan are considered wards of the entire community, some more wild and some more domesticated. Whether personally owned or not, all dragons live out in the pastures and/or the lake, free to roam the town as they please (pokeball use is very rare within the clan).
Almost all members of the clan will help take care of the dragons at least once in their lives, usually as children and always under the guidance of the pokemon's official caretakers, called dragon tamers. Although major injuries are somewhat rare among tamers, the possibility always exists, so children and tamers-in-training are always supposed to be watched over very, very closely.
Aragoto is a sacral art, saved for important cultural ceremonies. They most often occur as religious rites, but they may also be performed at festivals as well. Productions always tell the story of a historical event; though contemporary historians may argue that these plays are more akin to fable than real-life events, the Clan views it as completely accurate to their heritage. To be chosen as an actor is an honor of the highest regard, and to make a blunder while performing is the highest disgrace (well that's a little exagerated but still). Therefore, actors will often dedicate most if not all of their free time to perfecting their roles before an upcoming performance.
Kumadori, though an important part of aragoto, is not restricted to the practice. It’s most like a culturally significant face paint, applied at home before attending festivals, ceremonies, and celebrations alike. Most clan members will have their own personalized kumadori, though to choose any decorative colors other than red and black is extremely rare due to the associated meanings.
Although full kumadori is not normally worn in day-to-day fashion, many clan members like to reference it in their own makeup and consider it to be a source of personal pride. The most famous examples include Lance and Clair of the Indigo League, who wear partial kumadori as part of their League uniforms. Additionally, Clair is one of very few clan members in the entire clan's history to purposefully wear blue kumadori outside of aragoto.
The Blackthorn Gym has traditionally been run by the Dragon Clan. Although there are select people who may find this unfair, its historically been one of Johto's most successful gyms, and there's no rules against nominating another clan member as the next gym leader as long as they are approved by the Pokemon League.
Drinking is heavily frowned upon within the clan, so ingrained in their culture that most clan members who move away will continue to abstain long after they leave. Of course, the reason why is obvious: they've willingly surrounded themselves with some of the most notoriously dangerous and unpredictable pokemon, and to accidentally slight one of these beasts could very well end with catastrophic consequences. Most clan members will end up with the occasional knick and scar, sure, and the dragon tamers will often wear their injuries as badges of honor, but no one wants to end up as the next cautionary tale. Unfortunately, accidents still happen with every new generation, even within the Elder's own family…