In Japan, the Big Fancy House takes a meaning well beyond what it does in the US or UK. Japan is a very densely populated nation — equivalent to packing half of the USA's population in a space roughly the size of Montana — which results in some of the highest real estate prices in the world. This is doubly the case in Tokyo and other big cities where even the smallest homes can cost 100 million yen ($1 million US) and up. Consequently, a large home with a lot of space around it is fantastically expensive, and indicates its owner has more money than the rest of the cast combined.
If the front door is more than a few feet from the street, if there are more than four or five rooms, if the rooms are bigger than the typical American walk-in closet... you are looking at the residence of somebody with wads of cash. If it looks like a French chateau and is surrounded by an actual estate, then we are well out of filthy rich and into Fiction 500.
This doesn't stop many manga-ka from driving the point home by giving their characters homes opulent beyond Versailles, however.
A family that is extremely traditional will invariably have The Thing That Goes Doink somewhere in the yard of their Big Fancy House. It may also be found on Middle-of-Nowhere Street.
This is not so much a Japanese Media Trope as a fact of Japanese economics, but it makes for a great visual shorthand when the animators want to let the viewer know someone is outrageously wealthy. The same premise usually applies to characters mentioning their family has a summer home somewhere.
Midoh in Asagiri no Miko lives in a comically exaggerated Big Fancy House that puts the Palace of Versailles into shame - it has individual rooms whose back walls disappear into the horizon.
Chiyo-chan's spacious, walled-and-gated, far-off-the-street house in Azumanga Daioh is a source of much wonderment for her friends, who had no idea she was so wealthy until they visited. And she has a summer home.
Tomo's response on reaching the gate: "M-Maybe we should have brought a gift?"
Many characters in Card Captor Sakura have big houses, the less fancy one belonging to the Kinomoto family. Sakura's dad is a famous archaeologist, her Missing Mom was a famous model... however, they weren't always that well-off, having lived for some years in a cosy but small apartment. They only moved into that house around three years ago, when they arrived to Tomoeda: by that time, Nadeshiko had already died and Fujitaka had only begun to make himself a name as an uni professor.
Pictured above (and once on the main page): Tomoyo Daidouji, being the daughter of a toy-company CEO, lives in a classic Big Fancy House; Tomoyo's bedroom is bigger than the entire second floor of Sakura's house. And then are the mansions in England and Japan where Eriol lives, and, in the first movie, the big estate of Shaoran's family in Hong Kong. And don't forget Great-Grandpa Masaaki's HUGE own European-style country mansion, either!
When the gang of Code:Breaker needs shelter for the night, the apparently homeless Yuuki suggests a bench, then a park, then the big fancy house that envelopes the park. Naturally, it's his house (big imagination + The Nicknamer + a country that loooooves collectible toys = (mega) profit!). When Toki suggests that Yuuki is just being used to make a profit, Yuuki shows that he's also really good at reading the stock market not that any of that helps with what he really wants: friends :(
The Student Council in Code Geass has its own entire fancy house, and then there's the rest of the academy.
And we're not counting the imperial villages and castles as well.
In Death Note, Yotsuba Group's Shingo Midou has one of these with a large front yard. His living room was redecorated in the anime but his TV remained tiny. The Yagami family house also qualifies, as does the HQ/apartment Light and Misa live in later on.
Note that Ruki's mother does not own the Big Fancy House; it more exactly belongs to her mom, Ruki's maternal grandmother Seiko.
In Eden of the East, amnesiac Akira Takizawa is quite surprised to learn that he apparently has a fully stocked supermall to himself. To be fair, it's assumed that its property values were unusually low thanks to its proximity towards a missile disaster zone, but still - fully stocked supermall.
Einzbern Castle in Fate/stay night only has four inhabitants, nevermind that Berserker is one of them. Has its own forest too.
Actually, except for during the Grail Wars (of which there have been five in about 200 years, and which last at most two weeks), it has no inhabitants. The Einsberns own the castle for the sole purpose of providing a base for whoever is representing them in the war, and Ilya only moved there from Europe a few weeks ago, at most. Yes, they're that rich.
The houses of the other three main (human) characters (Shirou, Rin and Sakura) are also rather large. In Rin's case, however, she's implied to have rather little actual spending power, because she spends any spare money that she has on jewels (for her magic).
To be precise, Sakura and Rin both live in Western style mansions; dimensions and size are never explicitly pointed out although both are LARGER then Shirou's home. Shirou, on the other hand, lives in a Japanese style mansion that has 4 separate buildings (Main, Out, a Dojo, and a Large Shed) that is stated to have enough rooms to serve as a hotel.
The Sohma family in Fruits Basket has an enormous gated compound with multiple roomy houses. The house that Yuki, Shigure, and Kyo share doesn't seem especially big, but it is in the middle of a huge plot of undeveloped land.
The Armstrong manor in Fullmetal Alchemist. Mustang comments to Olivier that it's so big, she could hide an army in there. And that's exactly what she does.
Honoka Yukishiro's home in Futari wa Pretty Cure is a traditional Japanese dwelling with a garden and walled yard, but is also located in the middle of a city; upon just seeing the gate Nagisa realizes that she's way out of her economic stratum. Same goes for Komachi's digs in the fourth series.
Karen, from the same series as Komachi, could probably buy Honoka and Komachi's combined assets with her pocket change. Not only is her home positively huge even by American standards, but it's not all. She has a smaller house just sitting around completely unused, which she just gives to Coco and Nuts to live in like it's nothing. At the start of the second series, that house is unavailable... so she gives them another one.And she has a summer home. On her island. Are you getting the picture here?
Just in case you weren't getting the picture, the second season later also shows us her mountain villa.
The Randoll estate from Future GPX Cyber Formula is one, which is complete with a garden the size of a forest and it even has its own race track.
The main house of the Gowa family in Gasaraki, a very traditional place indeed.
What little we see of Madoka's house in Get Backers implies it to be very large; she has room for all of Shido's animals on her lawn, and Akutsu Shunsuke, the man Shido was working for when he met her, definitely applies. Flashbacks show Kazuki's family's home to be even bigger and fancier.
In the episode ¥?$ of Ghost in the Shell: Stand Alone Complex, the team visits an eccentric billionaire's mansion to save him from a hitman. It's absolutely ginormous, with a large estate around it. Another sign of his wealth is the wall-to-wall stacks of gold bullion in his bedroom.
Kazuharu Fukuyama from Girls Bravo owns a Big Fancy House so large that it has an elevator. Along with that, his family also owns a multi-billion dollar stadium, an entire gaming company, and an entire mountain range.
In the second live action series of Gokusen, Yankumi tries to track down a chronic absentee student only to find he lives in a ludicrously large house, and his neighbors apparently feel the need to speak about his family in exceedingly obsequious Keigo.
The very first student Great Teacher Onizuka helps is a girl whose family lives in one of these, but she's unhappy because the once lovey-dovey family has become emotionally distant now that they've upgraded from a one-room apartment. Onizuka's solution? Literally bash down the wall between her parents' rooms.
The mansion in Hanaukyō Maid Tai is so big, they're able to park a blimp in the driveway. With plenty of room to go around it.
Sanzenin Nagi in Hayate the Combat Butler has a massive mansion, plus tall walls that surround the grounds, that is about the size of downtown, so ridiculously large that a lake, space center, and theme park can fit into it. This is especially to the shock of Hayate, who has been living a poor life prior to working for Nagi. And Nagi says that, as not many people live here, it's SMALL. Then, when they visit Nagi's grandfather, when Hayate sees HIS mansion, he's convinced he's no longer in Japan.
Athena Tellos also lives in a huge and very fancy mansion. In fact, Hayate utters the quote above as he goes searching for her after Nagi smashes her inheritance stone, which also was a Mineral MacGuffin related to Athena's Superpowered Evil Side.
Hayate ends up blowing Athena's mansion to kingdom come. She's not exactly happy about it, but has more important things on her mind, such as her release from said evil side and being reunited with Hayate.
In Hayate the Combat Butler case it's not an extreme show of wealth, since all but a few of the cast have homes that fit squarely within this trope. Just none as large as Nagi's is shown to be. They're all filthy rich.
Hayate has the same problem navigating Nagi's 'small' mansion at times equal to the trouble he has navigating Athena's.
Yoshitaka's house in He Is My Master is positively enormous, taking up what seems to be a hundred city blocks on a side, with its own small lake and stream, as well as a very large house filled with expensive treasures. What gets broken each episode would pay for a decently-sized house.
Saya Takagi from Highschool of the Dead lives in a what could only be described as less of a palace and more of a castle. Her parents are fabulously rich ultranationalist Crazy Survivalists, so of course their house is built like a bunker and has it's own shielded power plant and a small army of guards (in addition to being amazingly luxurious on the inside, of course).
The Battour estate in Kaze to Ki no Uta as well as the chateau 'Cherubin de la Mer', especially the latter (to the point that Serge, the heir to the former, was awestruck by it). Although note that the Japanese economic implications don't apply quite so strongly as the series is set in historical France.
Momoka on Keroro Gunsou lives in a huge mansion with an on-site shopping plaza and other absurdly luxurious accommodations. Dororo's family also had a Big Fancy House on his home planet. The Hinatas also have a reasonably large home (in inner Tokyo, no less), but for an obvious reason.
The Momoka estate has apparently been granted sovereignty by the Japanese government. It even maintains a heavily armed private security force to defend against all manner of conventional and supernatural threats.
In Living Game, Raizo briefly has the opportunity to date someone living in a huge mansion. His regret on not marrying into money is tempered by finding out she uses most of the house to house her pet snakes, though.
Ayaka's family home in Mahou Sensei Negima! could have been built by Louis XIV. But Konoka's home in Kyoto trumps it — it's not just a Big Fancy House, it's an entire temple complex staffed by priests, mages, and a dozen or more maids/shrine maidens who treat her like a princess. And then there are Evangeline's numerous estates, which consists of at least a castle, a summer resort, a hot spring, as well as other areas used for Negi's training. Impressive considering that before it became as it is today it is implied she dug them from her real land.
To the Japanese audience, the isolated two-story log cabin (somewhere on the huge school grounds) Eva apparently lives in was already noteworthy. Although it was probably meant to carry subtext that the school really doesn't want her having to room with the students... or them with her.
Sachiko's mansion in Maria-sama Ga Miteru is remarkably big. Interestingly enough, her summer house is much smaller, Sachiko remarks that she prefers it as it gives her a feeling of comfort because it is cozy. Sachiko's fiance Suguru also lives in a very large mansion.
The home shared by the Koshikawa and Matsuura families in Marmalade Boy is large enough for the six of them to live together comfortably, but the house Meiko Akizuki's family lives in dwarfs even that, and Miki herself says that when she spends the night there. Miwa and Suzu also live in rather fancy houses, understandable since their fathers are famous architects.
In Mars, Rei's father lives in a more realistic version of this; Rei and Kira move into it after Kira runs away from her place. It's full of flashback fodder for Rei's childhood, such as the room in which his mother hanged herself and the room still crammed with his dead brother Sei's paintings. Consider then, that Rei's dad has been living in this huge house alone with all of these reminders about his family's tragedies.
The estate where Midori and her mother live in Midori no Hibi is almost as large and impressive as Ayaka's.
The Hyuuga and Uchiha households in Naruto: Very big, to the point of almost being a town within a town in the Uchihas' case, very traditional, The Thing That Goes Doink sounding off in the background. Used to convey power and tradition more than loadsacash We eventually learn there was a reason the Uchiha were kept in one area.
Whenever the action is in a private home in Oishinbo you can be certain that it is in one of these.
Given the nature of the protagonists of Ouran High School Host Club, it's no surprise that all of them except Haruhi live in enormous European or Japanese-style mansions. Haruhi, by contrast, lives with her Hot Dad in a two room apartment that's actually smaller than their club room.
Similarly, the Tendo home in Ranma ½ is a positively huge traditional-style Japanese complex featuring a two-story house and a detached training hall surrounded by a large yard and bordered by a stone wall. The Kuno estate is even bigger, being almost a medieval Japanese castle. Both of them supposedly exist in the center of the resolutely middle-class Nerima district of Tokyo...
Of course, popular Fanon has it that the Tendo and Kuno family homes are simply old family-owned homes that just haven't really changed with the times (it certainly seems likely for the Kunos).
In the Sailor Moon manga, Ami Mizuno (Sailor Mercury) brings her friends home to a place they immediately call an example of a millionaire's home, with a marble foyer she tells them not to worry about when it accidentally gets cracked. While the anime and live-action series don't play this up as much, her mother remains a doctor in all versions, the ostensible source of the wealth.
Rei Hino (Mars) lives in a huge Shinto shrine, which seems to be built in the old traditional style.
The non-canon Street Fighter manga Sakura Ganbaru! depicts the Kanzuki Estate as so large, it doesn't just have its own rivers, mountains, and savannas, it has its own climate. Even though it's in the middle of Tokyo, visitors don't arrive by car, they arrive by chartered plane and land at the private airstrip.
In the also non-canon Street Fighter Alpha Generations OVA, Gouken and Akuma's master Goutetsu lived in a huge-ass Japanese traditional complex. The only persons living there are these three alongside the housekeeper, a young woman named Sayaka.
Subverted in Summer Wars, where the Jinnouchi family's mansion is all that remains of their wealth.
Tsuruya's villa in Suzumiya Haruhi. Apparently, there is nothing it doesn't have. Kyon's first line in the anime upon seeing it is wondering what evil he has to commit to be able to live somewhere like that.
In Tenchi Muyo! GXP, the unlucky hero Seina discovers that his family was able to afford a new Big Fancy House by the time he returns to Earth after being shanghaied into the Galaxy Police. Fortunately for his self-esteem, it's as much because of the money he'd been sending home as their not having to deal with him jinxing their store.
It's still smaller than the one that Amane lets him stay in, though. He notes that his entire old house could fit in one bedroom. And that's just her family's summer home.
The Masaki home is nothing to sneeze at, either, although being moved wholesale onto the grounds of Yosho's shrine and rebuilt several times since doesn't hurt...
The Jurain royals are an unusual example in that they are filthy rich and live in trees. Trees with huge hollowed-out rooms and baths inside.
The Mendo estate in Urusei Yatsura actually is a medieval Japanese castle, somewhere in the middle of Tokyo.
...as heavily fortified as Fort Knox; land mines, watchtowers with spotlights, secret passages, vaults with timed locks, etc.
Youta Moteuchi from Video Girl Ai lives in a house that is both this and a Cool House. Sort-of justified in that Youta's father is a very well-known architect, and Youta himself wants to follow in his footsteps and become an artist.
In Yamada Taro Monogatari, after one of the students found out about the fact that Yamada is actually poor and planned to prove that Yamada is truly in poverty. Thankfully Deus ex Machina saves Yamada from certain disaster as his dad's best friend owned many holiday homes and planned to let them stay there free of charge. Yamada isn't too happy living there though, prefering the cramped home.
The residences of Shinichi Kudo and Professor Agasa in Case Closed are this. In fact, after Shinichi got shrunk into Conan and went to live with the Mouris, Ran and Sonoko had to drop by once in a while to get it clean, and later uni student Subaru Okiya (whose apartment was burned down in the case he appeared) moves in and becomes its landlord.
Yasuko from Aoi Hana lives in a large estate, which her girlfriend Fumi found out when she gets invited to meet Yasuko's mother and sisters. Luckily all the residents appear to be normal and well-natured folk. It's just too bad that Yasuko chooses that day to dump Fumi.
Mugi from K-On! appears to live in a huge mansion. We never get to see it, but Sawako-sensei was impressed when she drove Mugi home one day. Since Mugi claims that her family's beach estates are small, we can get the idea that her home must be huge indeed.
Madoka's home in Puella Magi Madoka Magica, with a very big and empty-looking bathroom among other things. It's hinted that it was built by friends of Madoka's parents.
Also, for someone who lives alone after her parents's deaths, Mami Tomoe's apartment is huge. (If, in the original TV series, rather empty. The Blu-Ray release makes it much cozier.)
Spain and young!Romano (and maybe Belgium and Netherlands too) live in a castle. Justified Trope, this is Imperial!Spain we're talking about.
Subverted in the case of Chibitalia, Hungary, Austria and HRE. Austria's mansion is pretty big, but the end of the Chibitalia strips suggests (if not outright states) that their spending wealth is very limited, which is remarked when HRE leaves the mansion with other Germanic states. OTOH, the fancy manse where Austria and Hungary interact with Maria Theresa plays this straight, which is again a Justified Trope considering that Vienna is very famous for palaces like Belvedere or Schonbrunn.
In the manga, the Nordics gathered for lunch and Iceland's "announcement" in a house that looked pretty average-sized. In the anime, said house is much bigger. It's not clearly stated who it belongs to, but since Iceland is the one who asked them to gather (and we see his puffin having lunch as well), he's the most likely option.
Switzerland and Liechtenstein seem to live in a rather cozy home, too.
In Yu-Gi-Oh Season 0, the True Companions get the shock of their lives when they see Kaiba's house, complete with a hedge maze modeled after the Palace at Versailles. Jounouchi/Joey says "His house is HUGE! There must be a law about living in a house that big!".
The Kuchiki Manor (aka Yachiru's playhouse) is so big and fun that Yachiru (in omakes) has modified it with hidden doors and tunnels and holds the Women's Shinigami Association meetings there much to Bya-kun's chagrin. It wasn't, however, big enough to hide the enormous swimming pool the women decided to build and "hide" smack in the middle of his yard. Hilarity ensued.
Shukuro Tsukishima lives in an European mansion located in the woods surrounding either Karakura or Naruki. Not to mention Yukio seems to own the whole building that is used as the X-Cution HQ.
Flashback arcs reveal that the Ishida Manor is a huge sprawling house on its own private land somewhere in Karakura Town. It came complete with servants, too. One of them being the maid Kanae Katagiri, who'd become Ryuuken's wife and Uryuu's mother with time. This was Souken Ishida's home and where Ryuuken lived as a child and a teenager. Uryuu's memories of Souken imply Souken had a much smaller home by the time Uryuu was born and Uryuu's classmates have commented that Uryuu is very poor. Since Uryuu refuses to live with his father, and Ryuuken's current home or wealth status has never been revealed, the current state of the Ishida family's wealth and residency is a complete mystery, but until not too long ago the family was clearly fantastically wealthy.
Yuri Tokikago also lives in an awesome loft located in a VERY high-class condo, which amazes Shouma when he and Ringo drop by. Her boyfriend Tabuki moves in there when they get engaged... and then the Attempted Rape of Tabuki by Ringo happens. And several episodes later, when Tabuki gets Put on a Bus, Yuri is living there alone again.
Killua Zaoldyeck lived on a massive estate with his family, a bunch of world-class Assassins before he ran away to become a Hunter.
How big is it? The mere front is more than enough to count as the local tourist attraction. And when Gon manages to get in, it has an impressive front yard and luxurious gardens as well as the building itself.
In InuYasha, Sesshoumaru's mother (an insanely powerful and hot youkai queen) possesses a huge, sprawling traditional Japanese palace. Location? Floating amongst the clouds. It takes even someone with Sesshoumaru's insanely good nose a good few days of active searching to actually find it and even then his mother has to come to meet him before he can locate it. His mother must be an absolute bitch to get in touch with at short notice.
As a little boy, Inuyasha is shown living with his own mother (a human noblewoman named Izayoi) in a more normal traditional Japanese palace. By "more normal", we don't mean "small": it had huge gardens and at least three separate buildings.
There's also a variation in regards to Kagome's house. If we count solely the living space, it's a normal two-store house... but if we consider it's located inside the grounds of a big Shinto shrine that is located atop of a small hill, then the size increases quite a bit. In fact, when Kagome's father died in an accident and her grandmother (the old priest's wife) followed soon afterwards, the Higurashis moved into the shrine to keep company to the grandfather.
In Oniisama e..., Fukiko and Takeshi's family have several European mansions, complete with greenhouses, rose gardens, huge pools, picturesque forests, and the odd Room Full of Crazy to even everything out.
Also, for a middle-class girl Nanako lives with his parents in a pretty large house. Likely to contrast with her "Oniisama" Takehiko's rather simple bachelor apartment and Rei's flat with a Room Full of Crazy.
Mariko and her mom Hisako live in a really nice home too. After the Shinobus's divorce, they move out into a cozy but small flat.
In Eden No Hana, when Tokio Wakatsuki moves back to Japan to find sister Midori and rebuild his life in his home country (after almost one and a half decades in the USA), he invokes the trope via intending to purchase a really big house for the two of them. And yup, the one in which he and Midori live is pretty big and cozy per Japanese standards.
Kuro's house in Kodomo No Jikan. Justified, as she's extremely rich (she has a Gold Card at 10 and a 4 poster bed with a room that puts American master bedrooms to shame).
Subverted in Tenkuu Senki Shurato. The house in which Shurato lives with his parents, sister and grandfather is pretty big by Japanese standards (and is in the middle of Tokyo, meaning the grounds where it's located can be pretty expensive), but it seems to also be very old. It may be yet another old family-owned home that just hasn't really changed with the times.
Marble Mansion, the Russell's huge manor in Lady. Which is sold-off later since they're also Impoverished Patricians... and that becomes a plot point in the sequel Hello!Lady Lynn as Lynn's rival Mary manipulates Lynn via promising to help her get it back — but only if she relinquishes her bid to the Lady's Crest that both of them want so badly.
The home of Chairman Morinomiya in Gakuen Babysitters, which Ryuuichi and Kotarou now also live in after the plane crash that killed their relatives.
Love Lucky: Fuuta and Kirari move into one in the last chapter.
In Ten Yori Mo, Hoshi Yori Mo, both the Shijou and the Narumiya families live in big European homes (Though the Shijou's household isn't as rich as it used to be). In the meantime, the Fujiwara family resides in a traditional Japanese complex. This contrasts with the Mizumoris, who lived in a standard two-bedroom apartment before the story started and said condo got blown up, forcing Mio to move with the Shijous.
In Kotoura-san, Haruka Kotoura's grandfather Zenzan has this. When the ESP Club members went to his house in episode 4 to find Haruka, they have noticed they didn't even see the house from the entrance. This is even Played Up To Eleven in Episode 6 when the ESP Club members went there—turns out it has a private beach, and Zenzou built a theme park just because Haruka brought friends back for the first time...
In The King of Fighters: KYO manga, Kyo Kusanagi lives with his parents Saisyu and Shizuka in a huge traditional Japanese house located in the outskirts of Osaka. (And atop of a hill). It seems to be an inherited home mantained through the years and outfitted for modern use, as the backstory that took place 600 years ago shows parts of a very similar home owned by the Kusanagi ancestor and his clansmen.
In Sakura Gari, There are two of these in the lands of the Saiki family. One is a Western mansion that seems to be pretty recent, the other is a traditional and abandoned Japanese one used as a warehouse (almost surely the original home). This is very plot important, as Sakurako was locked away for nine years in the latter, and many things happen there afterwards. And in the second-to-last chapter, Sakurako burns it down to kill Souma and Masataka.
Dr. Katsuragi lives in a huge traditional Japanese home near the city. Which gets burned down, with him inside.
In Fairy Tail, Lucy's former home was a large mansion. Her guildmates take it in stride, until they discover that the land outside the walls all the way to the mountains on the horizon is also part of the grounds.