Though canonically straight (and spoken for), Cloud is a favorite of the yaoi fandom, who ships him with just about every other male character from "The Compilation"; most often with Sephiroth, Zack, and Vincent. But thanks to Dissidia, he's also a favorite for crossover shipping, with Cloud/Terra and Cloud/Lightning both being popular fan pairings. So you can find plentiful amounts of fan art dedicated to them. And thanks to their appearance in Monty Oum'sDead Fantasy, he's also shipped with Yuna.
In Final Fantasy VIII, Squall seems to be pretty paired with everyone who isn'tRinoa. It's not like the game's entire plot revolves around them falling in love with each other or anything.
In Final Fantasy XIII, we have Lightning. Two major reasons for this are the fact that she has no canon love interest, and the game has a not-inconsiderable amount of Les Yay between her and Fang. Then there's her "motherly" relationship with Hope. If you want to go into Crossover Ships, there's Noctis, and being a Distaff Counterpart of Cloud Strife you can pair her up with him or any of his love interests.
She's also paired with the other party members quite often. Snow X Lightning usually interprets their clashing personalities and Lightning's initial hostility as Belligerent Sexual Tension and takes it from there. Some Sazh X Lightning pair start with them talking about their parental experiences. Oh, and there is some Lightning X Vanille too. She barely talks to Vanille in-game. Her crossover pairings more than doubled after Dissidia Final Fantasy.
In Final Fantasy XV, Noctis gets paired up with just about everyone. There's his official love interest Lunafreya, Iris who has a crush on him, his three friends whom he shares Ho Yay with, Nyx from Kingsglaive: Final Fantasy XV (despite only meeting him once offscreen), temporary party members Cor and Aranea, as well as Foe Yay with his enemies Ravus and Ardyn. Heck even the pairing of him and Talcott has a fandom (although only once he's an adult). And of course there's the aforementioned Crossover Ship with Lightning.
Following somewhat close behind her, there's Squall, who for some reason seems to be paired a lot with several characters.
And in Japanese fandom, the one who stands head and shoulders above ALL of them is Firion, for some inexplicable reason. He is paired with everyone. It's the Rose. That rose has been in the hands of at least nine characters throughout the course of the two games. In fanshipping land this automatically means he is paired with everyone who has obtained it. People even ship him with Aerith for their mutual love of flowers, even though the two have never canonically met! However perhaps the only pairing that has any real basis in the events of the games is Lightning, due to their undeniably cute scene in the reports(turns out he just wants that pesky flower back but still who wants to crush a shipper's dreams!)
Lightning's paired with a fair amount of men in Dissidia's sequel (technically prequel), too. Mainly, Kain Highwind, Firion, and the Warrior of Light.
Minamimoto: Why, hello there! This mic is zetta sexy!
Also calculators and math books.
Joshua too. Although Neku is by far his most popular option, he regularly gets shipped with Hanekoma, Minamimoto, Kitaniji, and Rhyme. Shiki and Beat are rarer but also exist, and he's a favorite for crossover ships.
Applies to all of Persona's player protagonists since the third game, with both the male and female protagonists of Persona 3, Yu Narukami of Persona 4, andJoker of Persona 5 having been paired with virtually every other cast member at one point or another. Somewhat justified since building relationships has been a major part of gameplay since 3, including the option to romance characters of the opposite sex (with Joker in particular being able to romance even adult women); it's even possible in-game for the player characters to build an outright harem (though you'll eventually be punished for it in Persona 4 Golden and Persona 5).
Crossover Persona Q: Shadow of the Labyrinth only added fuel to the fire, thanks to a fake wedding ceremony scene where Yu and the P3 protagonist have the option to "marry" anybody from 3 and 4's main cast regardless of their gender (even Heroic Dog Koromaru).
Emil seems to be this, too—he's been paired with a good chunk of the new cast including Ratatosk and Aster (who Ratatosk killed about a year and a half before Emil even came into existence.) Plus several of the original cast.
As far as Tales of the Abyss goes, Luke/Everyone might as well be canon. ... Well, everyone important. At the very least you cannot deny that Luke/The Party (or The Party/Luke, as it is...) is very nearly canon.
If you are a Tales of Vesperia character, the fandom has decreed that you want to have sex with YuriLowell. Period. He's probably most often shipped with Flynn, but Estelle and Judith aren't far behind...and then there are people who ship him with Raven or Duke or Rita or even Ioder, and, appropriately enough given the above, Yuri/Luke is a popular crossover pairing.
Tales of Xillia 2 has two, in both Ludger, the new silent protagonist, and Jude, whose Ship Tease has gone Up to Eleven since the last game. They get shipped with each other, of course, but Jude also gets shipped with Alvin, Milla, Ivar, Gaius (thanks, Hot Springs ending), has a canonical alternate-universe-bird-spirit boyfriend (it's complicated) and even gets some Ship Tease with Elize in a victory quote. Ludger gets shipped with Alt!Milla, his brother, Nova, and...pretty much every member of the playable party since they've all got relationship values now. It's madness.
Fire Emblem: Thanks to the support mechanics, most of the cast falls under this, with the fandom merely taking this up to eleven.
In Fire Emblem: The Binding Blade, there's Roy. He has six possible wives, subtext with two girls he can't support, and can support with 4 other males, one of which is his milk brother (or male maid), and is obviously a target for Bodyguard Crush. Not to mentioned that he's often shipped with the other fighters on the Super Smash Bros.. Melee roster...
Roy's got some brutal competition for the "Pimp Lord of Fire Emblem" from Seliph in Fire Emblem: Genealogy of the Holy War, who can take to his side one of fifteen possible wives (seven female second-gen characters and their potential replacements, plus Yuria).
Lyndis from Fire Emblem: The Blazing Blade already has four canon love interests (five if you count Florina as one). Also, Sain and Wil are considered extremely plausible lovers, Karel/Lyn and Lyn/Ninian have niche followings in the fandom, and one author even managed to pair her with Renault and make it plausible. There's the infamous Lyn/Tactician fics.
My Unit (or Kris) in the remake of Fire Emblem: Mystery of the Emblem is an in-universe Launcher, capable of supporting with the entire cast of the game. They don't have as many potential love interests as Roy or Seliph, though; male MU has three, and female MU has five.
The My Unit (or Avatar as s/he's called in the west) from Fire Emblem Awakening takes this one step further. S/he can marry any player character (including the Paralogue characters Gangrel, Walhart, Aversa, Emmeryn, and Ike's descendant Priamand the Child characters like Lucina, Nah, or Yarne... and yes, s/he can have a kid with them), provided they're of the opposite gender.
Heck, the only Awakening characters that can't be paired with everyone else in-game are pre-promotes like Say'ri, Tiki, Anna and the SpotPass characters. And even that doesn't stop fans from coming up with their own fanon ships.
And now Fire Emblem Heroes... oh GOD. It already has an INCREDIBLE amount of characters from all over the Fire Emblem universe (with the implication that they're planning to eventually incorporate EVERY SINGLE CHARACTER in the franchise) and there's a support system with the player character summoner (comparable to the tactician from Blazing Blade) and between characters. Therefore, ANY ship is possible.
The Legend of Zelda: Link is easily the video game town bicycle; he's paired with everyone from the eponymous Princess Zelda to... well, to the Shinto goddess Amaterasu as seen in wolf form in Ōkami, given that Wolf Link from Twilight Princess is one of Link's most famous incarnationsnote If there were a Shinto Hell, whoever first did that would be going there. Nor is this the only strange ship involving Amaterasu, in or out of Okami itself. It doesn't hurt that Link tends to be an in-universe Chick Magnet who gains a new harem with each major entry. We've got the Ocarina of Time Harem◊, the Wind Waker Harem◊, the Twilight Princess Harem◊, and much much more!
In Golden Sun, everyone is a Launcher of a Thousand Ships.
And then the Lighthouses are jokingly considered as such in both the phrase's literal and other metaphorical sense, thanks to the fact that more than a half of the non-crack pairings (and a few crack ones) get their biggest Ship Tease in them.
World of Warcraft fan fiction's poster girl is Lady Jaina Proudmoore by far. She's often shipped with Arthas (pre- and post-undeath), Warchief Thrall (a pairing once characterized on the official Blizzard WoW General Discussion Forum as "Bow-Chikca-Lok'Tar"), a triangle between the three (and I'm sure a ménage à trois has been done at least once)...every fan fic writer who writes about his own PCs will have them meet Jaina at some point.
Jaina/Arthas (pre-undeath) actually is canon: they used to date when they were both teenagers.
And yes, they did sleep together. They would have married too, if not Arthas decided they both should finish their studies first. And when they were done with that, there was that whole undeath plague...
Kael'thas Sunstrider! He canonically had a crush on her (although it was apparently unrequited).
Jaina was heiress to the throne of Kul Tiras before the fall of Lordaeron, and Arthas and Kael'thas were both crown princes of their respective allied kingdoms. Given how royalty is often married off to allied royalty, its not surprising that she'd have been socially introduced to every male heir in her age group from every ally Kul Tiras had.
Outside of canon characters, elves in general seem to fill this role. Especiallyblood elves.
And as of Patch 5.1 and the Tides of War tie-in novel, Jaina is canonically hooked up with Kalecgos, who is literally a dragon.
Rinnosuke Morichika, being The One Guy, seems to get this treatment by default unless he's being portrayed as the Memetic Molester. If you scroll down this page, you will see a chart that breaks down his ships with every character in the series by source material.
Though specially Marisa, with more than seven frequent pairings, is who stands out in this trope. In some works to GAR levels.
Metal Gear's Snake tends to be paired up with almost everyone in the series, and outside of it - even before his appearance in Brawl. It really doesn't help that he's the Prince of the Even the Guys Want Him trope (Big Boss being the king).
In the MGS fandom itself, Otacon's probably earned this. He's been paired with Snake, Mei Ling, Raiden, Liquid, Grey Fox, Big Boss, Mantis, and young Ocelot, time paradoxes and plausibility be damned.
Sonic and Tails in the Sonic the Hedgehog series go with everyone... even though they show the least romantic interest of the entire cast.
As one fan put it, "If it's breathing and in the Gyakuten series, it'll get shipped with Edgeworth. It's inevitable". However, in Spirit of Justice, Edgeworth makes clear that he's got absolutely no intention of marrying anyone.
Disgaea has a rather small shipping base, in that most of its characters are only commonly shipped in one or two pairings each... the second pairing usually being with Etna. Seriously, Etna gets paired with everybody, including but not limited to: Laharl, Flonne, Mid-Boss, Adell, Rozalin, Axel... even the Prinnies.
Team Fortress 2 - The poor Scout doesn't get a break when paired up with any of the other classes, not even his own. There's also the Pyro, who may be female. The Medic (usually a Memetic Molester) occasionally gets this kind of characterization due to his status as a Support class and the fact that he racks up points the fastest via assisting other classes, as well as the fact that his gameplay role is that of the White Mage and therefore Yaoi Fangirls designate him as the de facto Uke when Scout's not filling that role.
Mega Man (Classic): Poor, poor Splash Woman. It doesn't help that she's one of the only two lady bots in a cast nearing 100.
Looking at the fan art, Metal Man gets this treatment too.
In general, ANY Robot Master, including the Rockman Killers and the Stardroids. Each of them have launched enough ships to make a tangled love web. Perhaps the most common: little Mega Man himself!
Like their brother, Roll and Proto Man also have launched their own fleets. Proto Man is especially popular judging by the sheer volume of fan art and fiction that exists. In Roll's case, she gets paired so often for the same reason Splash Woman does.
Mega Man X: X and Zero might be the two most shipped characters of the franchise.
X has been paired with Alia, Nana, his love interest from the manga Marty, Berkana because of the Foe Yay, on ocasion with Axl for thoses who prefer Ho Yay, and even Vile. There's even a couple of fan-art of X with Iris, Zero's love interest.
For Zero there's the canon pairing with Iris, Layer because of shiptease Axl. Ciel or Leviathan from Mega Man Zero. One can even find pics of Zero and Roll.
Heavy Rain: Norman Jayden, the only one of the four heroes without a canonical love interest, is consequentially paired with everyone in the game, from Ethan Mars to Carter Blake.
Leon Kennedy, of Resident Evil is a classical Type A, sometimes even to the point of Even the Guys Want Him among players. His canon love interest is Ada (and to a lesser extent, Angela, who appeared once and then was Put on a Bus), but he's also regularly paired with Ashley, Claire, Jill, Steve, Chris, Wesker, Luis, Krauser, Hunnigan, Kevin, Manuela, Buddy, Helena, Sherry, and Mike the Helicopter Guy. In addition to the large amounts of zombie porn that affect all characters within the fandom and countless self-inserts. Admittedly, the fact that he almost always ends up with a female character for a partner and the fact that at least two of them seem to have crushes on him does not help, nor does his (failed) attempt to get Hunnigan's number.
Claire Redfield, however, falls quite neatly under Type B as the "kickass everygirl" who has no special training and a kind heart, but still keeps up with the rest of the characters. Her ships includes Steve, Leon, Ada, Sherry, Alfred, Wesker, Jill, Rebecca, Carla, and her brother Chris, though many crack pairings exist for whatever character the author deems most attractive.
As mentioned above in the discussion on Link, Ōkami's Amaterasu gets shipped with far, far more characters than a non-talking wolf should ever be. Most of these rely on Ammy having a human form that we never see.
This happened to Dawn and Lyra, especiallyLyra. The most popular characters to pair Lyra with (in Japan, at least) are Silver, Lance, Ethan, and PETREL. These are just the popular ones. In the west (and East at that), Morty and Proton are also often shipped with her as well.
Silver himself is a shipping magnet, too, especially when you factor in his Adventures manga counterpart.
With Pokémon Black and White, we have the male protagonist Hilbert, who's being paired with practically every female in the game (and plenty ofprettyboys.) On the opposite side of things, the female protagonist Hilda has inspired plenty of pairings as well.
The real winner of this trope, as far as Generation V goes, is N Harmonia. The fact that he's characterized as socially awkward has not stopped fans from pairing him with (drumroll): Hilda, Hilbert, both, Nate, Rosa, Bianca, Cheren, Serena, Red, Zoroark, and Ghestis!!
Red gets shipped with everyone, Pokemon and people outside the Kanto-Johto games included.
There's a reason a why a lot of players name their Ditto "pimp".
Protagonists in general get shipped with everyone. Calem and especially Serena from X and Y are no exception. They're shipped with all of their rivals, each other, Professor Sycamore, most of the gym leaders, Emma, the Big Bad...
Haseo of .hack//G.U., poor guy, virtually has a harbor reserved for him. From Atoli to Shino to Ovan to Endrance to Skeith to even the Grunties, he's been stuck with EVERYONE. Find someone that he HASN'T been shipped with.
Like Lloyd in Tales of Symphonia, Haseo is an actual canon launcher, since at the end of the third game, you can choose to "marry" (the characters are playing an an MMORPG) any party member, regardless of gender or even age. When trying to do it with a man, usually it leads to a "best buddy" scene rather than marriage, but there are a few exceptions like Endrance or even Azure Kite who want a little more than being friends...
She has her very own series by Saigado Comics, aptly titled: "Yuri& Friends", which pairs her with multiple characters from the KoF. Most often with Mai and Kingnote which is a nod to the fact that Yuri, Mai, and King were the original three members of the All Womens Team, but she's also been paired with Chizuru Kagura, Kasumi Todoh, and even her own brother, Ryo. Plus, there was a bonus crossover story featuring her with Capcom'sRyu and Sakura.
Chun-Li is the series' primary "go to" character when it comes to shipping, 'cuz she's hot plus she's canonically single. So fans can freely pair her with just about anybody, regardless whether male, or female. They're especially fond of pairing her with Ryu, but she's also been shipped with Charlie, Ken, and Guile (and to a lesser extent Cammy).
Ryu gets his share, too, despite his lack of interest in love life, being paired with Chun-Li, Cammy, Sakura, Juri Han, Rose, Ibuki (?), Makoto (??), Ken (oh boy)... and Bison? And maybe Sagat, that is, if he's not busy with his cornflakes.
Ellis from Left 4 Dead 2 ends up with everyone. Although 90% of the time it's with Nick, you can find him with his canon love interest Zoey, teammate Rochelle, Coach, the Hunter, the Witch, the Smoker and his friends that don't even appear in the game like Keith. Ellis will also usually be the target of any fanfic writer's Original Character.
Kasumi from Dead or Alive has ships for every base, ranging from the fairly mainstream Ryu Hayabusa, the more yurilicious Hitomi or Christie, all the way to straight up incest with her half sister Ayane or her brother Hayate. It would seem that whoever the favorite character is, shippers generally feel they go nicely with the cute redhead ninja.
Jin Kisaragi from BlazBlue. Aside from him being coupled with his older brother/rival Ragna the Bloodedge and childhood friend Tsubaki, Jin has been coupled with almost every character from the series even if it's almost impossible to happen. Despite him being a total asshole, this must be just a huge turn-on for the fandom.
Ragna himself enjoys a fairly substantial shipping base as well, having, in addition to Jin, been paired with Noel, Rachel, Taokaka, Nu (kinda-sorta), Celica, and several characters who aren't even from the same franchise.
Carl Clover also enjoys a fair amount of popularity amongst shippers as well, ranging from Noel and Makoto, to Litchi and his own sister, Ada, and, like Ragna, with several characters who aren't even from the same franchise.
Advance Wars has three. You have Eagle who gets all the good guys, Hawke who gets all the bad guys and some of the good guys, and Andy who gets it up the butt from everyone. ESPECIALLY Eagle and Hawke.
In Dragon Age: Inquisition, the player character can become this trope in-universe if they're a bisexual female elf. Unlike Dragon Age II, the love interests in Inquisition vary based on your character's gender, sexuality, and race. Most player characters have four romance options: two of the opposite sex, two of the same. A female elf, however, also has access to two more: Cullen (who is only into humans and elves) and Solas (who is only into other elves). This brings her total to six potential suitors.
Reptile seems to be working his way up, too. Although the only character that shows romantic interest in him is probably Khameleon (due to the whole Adam and Eve Plot thing), he's additionally paired with Mileena and Nitara on a somewhat regular basis. Apparently, the lizard man has moxie.
Chell has been paired up with nearly every character in Portal. Wheatley is paired with almost as many. And Chell/Wheatley is the most popular ship in the fandom.
As the only female character in Live A Live who can be brought to the final battle, and hence the only one who can canonically meet the protagonists from other eras, Li has been shipped across time and space. Popular love interests include Akira and Odio, but Masaru and Oboromaru are also occasional fic subjects, as is Yuan in the Fix Fics where they both survive.
Metroid protagonist Samus Aran easily falls into this due to not having any romantic interest in her own series (or more than a handful of characters per game other than herself, for that matter). Master Chief, Boba Fett, and Iron Man are common choices due to Shared concepts, but she seems to pick a new one up every new game in the Smash Bros series: Captain Falcon in Melee, Solid Snake in Brawl, and now Little Mac, due to the latter's introductory trailer, even though it primarily involved him punching the hell outta her for making fun of his height. Pikachu/Samus was a popular crack ship during Brawl but it usually wasn't presented too romantically. Also, oddly enough, Pit and Mega Man in the latter two games as well. It is not certain why parts of the fandom have deemed her a paedophile, out of all the characters.
Fire Emblem characters pretty much instantly get turned into this when they're revealed. Marth and Ike have especially been paired with everyone constantly since Melee, though it's most common to ship them with Link, Zelda, Peach, or each other.
This is inevitable for Bayonetta once she was announced and it's becoming apparent. For a dose of irony, the two earliest (and so far most prevalent) are Pit and Palutena.
When it comes to the younger characters, Ness is the most shipped. Ness/Red, Ness/Toon Link, Ness/Lucas, etc.
Sonic has been paired with nearly every female fighter since his first appearance in Brawl, along with quite a few men.
One would be quick to dismiss that Puyo Puyo doesn't have much ship fuel, being a puzzle game, but Schezo is paired with Arle, Rulue, Witch, Satan, Seriri, Lagnus, Incubus, Lemres, and Doppelganger Schezo, out of way too many characters to count. Yes, he ships with his own doppelganger. When he says "I want you!" did he really mean it this way? Nobody knows.
Sig is just as big of an example, with Amitie, Strange Klug, Klug, Arle, Lidelle, Raffina and Lemres only being the tip of the iceberg. Even characters who he has yet to interact with, like Maguro, Seriri, Draco or Doppelganger Arle are paired with him.
Due to the Player CharacterFrisk having no defined gender in Undertale, they are depicted as whatever gender needed to push a ship forward, typically female for the majority of ships, however some male examples exist, such as being shipped with Muffet or Chara.
Sans has been put with almost every character including Toriel, Frisk and/or Chara, Muffet, Papyrus, Asgore, and even Alternate Universe versions of himself.
Due to vagueness of the character interactions in Overwatch most characters are shipped with about four other characters. Somehow some characters avoid being shipped in general (Bastion, Torbjorn, and Winston) or are just so overwhelmingly shipped with one certain character that no one seems to even think about shipping them with someone else (Hanzo).
Mercy is currently shipped with the most characters which includes: Junkrat, Roadhog (or Junkrat and Roadhog), Genji, Soldier: 76, McCree, Widowmaker, Pharah, Zarya, Reaper, Mei, Reinhardt, Hanzo and Ana.
Zarya is shipped with Reinhardt, Mei, Widowmaker, Mercy, Tracer, Pharah, and Genji.
Strangely enough, Junkrat is this as well. He's been paired with Mercy, Roadhog, Mei, Symmetra, Lucio, D.Va, and McCree
Ana. Being one of the only characters with a known child, everyone speculates as to who Pharah's father was. The dialogue she has with most of her old teammates is full of Ship Tease, with all of them upset that they didn't know she was still alive, her complimenting Reinhardt and Soldier:76 on how good they look, and Reinhardt and McCree flat out flirting with her. Even Reaper is upset that she sided with Jack over him, which has fanned flames of a possible Love Triangle or Love Dodecahedron; after all, if fans can't decide which of the original team she slept with to conceive Pharah, then the next best thing is to assume she slept with them all.
Father speculation aside (which currently includes Soldier: 76, Reaper, and Reinhardt) she's also shipped McCree, Mercy, and Widowmaker. Also, she's currently the only person shipped with Torbjorn. This is especially impressive since she is 60 years old and completely averted Grandma, What Massive Hotness You Have!.
Died down even more with the Uprising event, as Ana's new spray shows her and her husband holding baby Pharah. Said husband's features look nothing like any other character.
McCree is been paired with quite the number of characters due to a large number of fans think he is attractive and his unique cowboy aesthetic. He's frequently paired with Hanzo, Symmetra, Lucio (all of whom he never met or interact with), his former superiors Reaper, Soldier: 76 and Ana, his former Overwatch fellow teammates Genji, Mercy and Mei, his former Deadlock gang member Ashe and Echo.
Almost every protagonist in every Danganronpa visual novel can be viewed as one as they are all pretty shippable with each other. As for non-protagonist characters, honorable mentions should go to these people.
Also, from the third game, Ki-bo is this due to his personality and him having No Biological Sex. The common ones are him with Miu and Kokichi. He also has been shipped with Kaede, Rantaro, Tsumugi, Shuichi, Tenko, Gonta, and Korekiyo.
In spite of all the major characters being animatronics, the Five Nights at Freddy's series has a lot of these, but out of all of them, Ballora takes the cake. She had been shipped with Baby, Funtime Freddy, Funtime Foxy, Ennard, Springtrap, the Puppet and even Bonnie and Freddy!
Siegfried, bar none has become this. Being the Soul series effective mascot (especially in his persona as Knightmare) and its main protagonist, Siegfried has been paired with practically every female character in the series at some point. His most popular pairings (from most popular to least) are: Sophitia, Hilda, Ivy, Tira, and Cassandra.
Sophitia/Siegfried is the series fan preferred couple, and it has gotten some support in official circumstances, what with the very few times the two characters have interacted in game being dripping with subtext: Sophitia collapses prior to the events of Soulcalibur after having a vision of Siegfried as Nightmare. In the same game, Sophitia shares a Destined Battle with Nightmare; Sophitia steps forward to challenge him and states her resolve with the words "I want to... save you," possibly implying she knows that Siegfried is Nightmare (or at least that Nightmare is really a tortured soul under Soul Edge's sway). Siegfried also rescues a captured Sophitia early on in the admittedly non-canon Legends (which would be set between Edge and Calibur) and she's one of three women to face Siegfried in his IV story right before his final battle with Nightmare (the others being Hilde and Ivy, who also have strong ties to Siegfried). VI also has Sophitia personally seek out a post-possession Siegfried for what is basically a re-enactment of the aforementioned Destined Battle, but despite the warm, vaguely romantic undertones in their scenes together, she's already engaged to Rothion. Speaking of whom, the only thing that seems to stand in the way of this ship is Sophitia's husband/fiance Rothion, who fans would like nothing more than to see die or otherwise removed from the picture (notably, while she is engaged to Rothion in Soulcalibur VI, she hasn't married him...yet).
Hilda also has strong ties to Siegfried, with her story in her debut game dovetailing with his and both character appearing in each others's story lines at some point. She works under him in her second game appearance, though he isn't the father of her kids.
Ivy worked for Siegfried while he was Knightmare, so the two have a deeper connection than the others and she was one of his final battles in his story mode in Soulcalibur IV. Their common nature as beings corrupted by Soul Edge make them stand out from other examples.
Tira fell in love with Knightmare (after Siegfried had abandoned the identity), aka Soul Edge, and spends a good portion of Soulcalibur III's story mode playfully teasing Siegfried in his story line about his time as the Azure Knight. She continues to playfully antagonize Siegfried in the subsequent game.
Cassandra is buxom, hot, and blonde, thus the fans have taken it upon themselves to ship her with Siegfried.
Sophitia, conversely, has become "the Siegfried" for the yuri fans; people have hooked her up with Taki, Ivy, Tira, and even her younger sister Cassandra. Tira make sense, since the girl is canonically obsessed with the heroine and her family, and Taki is the one who brought Sophitia home and brought her back to health after her battle with Cervantes. Ivy has the smallest connection to Sophitia, and Cassandra seems to be nothing more than wishful thinking on the part of the shippers.