Fire Emblem needs more pants. Which ladies wear pants anyway?
PD: I'm (finally) playing Fire Emblem Fates Birthright... So... I come here to ask about pairing suggestions.
I got you covered. I'll list off my recommend pairings by each male character in Birthright.
Male Corrin:
Male Corrin x Scarlet is actually a pretty good pairing. Scarlet is one of the Corrin-sexuals you'll get in Birthright, and she provides some great Strength modifiers to Corrin. This will be pretty useful since Corrin can only promote to Hoshido Noble for his default class in Birthright, and that class capitalizes Strength over Magic. The resulting Kana also gets some pretty good stat growths and modifiers to help in the Hoshido Noble department. It will also help you gain access to every child unit in the game if Corrin marries Scarlet, because due to the number of units you'll get, if Male Corrin doesn't marry a Corrin-sexual, you will miss out on one child unit.
I married Male Corrin with Azura in all three playthroughs though. Their support conversations are pretty cute together, not to mention the resulting Shigure and Kana will be pretty good.
Takumi:
Takumi and Oboro give great-pair-up bonuses to each other, and the resulting Kiragi gets pretty decent stat growths all around in addition to some good max-stat modifiers to his Strength, Skill, and Defense stats. Takumi and Oboro's supports are also really good.
Ryoma:
Ryoma has two good marriages that I can think of: Kagero and Rinkah. I married Ryoma with Kagero in my Birthright playthrough, and I got a pretty good Shiro coming out of it. He becomes a real hard-hitting monster thanks to the stat growth and max-stat modifiers she passes down; he can also potentially inherit Replicate from a Mechanist Kagero. Pairing up Ryoma with Kagero also gives Ryoma extra mobility if she is a Master Ninja, while Ryoma gives Kagero more Luck.
I've been hearing Rinkah makes a much better wife for Ryoma though, if not the best. She makes the perfect Pair-up bot for the Lobster Lord, giving him a good boost in Defense so that he has better durability against physical units, and the resulting Shiro gets decent stat growths all around minus Magic (but let's be honest, Shiro shouldn't really be used as a Magic-unit anyway). Rinkah!Shiro can also potentially gain Death Blow + Astra/Vantage from his parents, so there's that.
Saizo:
Now Saizo is an interesting unit. While he may be a ninja and thus a Strength-user, he actually has a decent Magic growth. This makes him a great user of the Flame Shuriken, a weapon that uses the Magic stat instead of the Strength stat (basically the Shuriken equivalent to the Levin Sword). Orochi gives Saizo a good magic boost so that he can wield physical weapons and the Flame Shuriken to his advantage, He also fixes Orochi's speed problem. Saizo's son, Asugi, also has good Magic growths, so having Orochi as his mother makes him even more deadly with the Flame Shuriken than his Father would. This was my Revelation pairing, though Sakura also works well with Saizo for similar reasons, except Sakura is much faster than Orochi by default.
Kagero is a great wife for Saizo if you want to go all-physical with Asugi. She also helps Saizo's speed issue. Well, Saizo may be a ninja, so of course he'll have good speed, but between him, Kaze, and Kagero, he's the slowest of the three. Kagero's speed boosts will allow him to get doubles more often. In return, Saizo is the bulkiest of the three ninjas with his solid Defense and Resistance stats, so Saizo can switch in to protect Kagero from the physical-oriented units should they go after her, while Kagero will handle the magic-oriented units thanks to her higher Resistance stat. Saizo and Kagero's support conversations are also among the best in Birthright IMO, one where you can really see their chemistry.
Azama:
I married Azama with Felicia in my Birthright playthrough, and it wasn't too bad. As a Great Master, Azama gives +3 Magic to Felicia, which can make her utilize a Flame Shuriken better due to her better Magic stats as a maid, or it makes her hit harder as a Strategist, Felicia's secondary class that is good for capitalizing Felicia's really good Magic stat. Strategist Felicia also gives Great Master Azama better Resistance and even a boost in mobility. Felicia is also one of Azama's few supports where he isn't a jerk, and is overall one of his best support conversations. The resulting Mitama gets decent stat mods as well; nothing too damaging. Mitama can also inherit Live to Serve, which is especially useful if you want to keep her as a healing class.
I heard Setsuna and Kagero also make pretty good wife options for Azama if you are looking for a more physical-oriented Mitama, but I'm not too familiar with either of those pairings to give more detail.
Kaden:
Moving on to Kaden, I married Kaden with Rinkah for my Birthright playthrough. Rinkah does a good job fixing Kaden's Defense issue thanks to her pair-up boosts. In return, Kaden helps boost her speed. He can also take care of magic-oriented units that would normally slaughter Rinkah thanks to her low resistance. The resulting Selkie gains some solid max stat modifiers all around minus Skill, and you can give her Death Blow to boost her chances of landing critical hits, which further helps fix that Strength issue for Selkie.
Setsuna also makes a good wife for Kaden. She gives him a little more Strength to get an extra edge, while she makes Selkie even speedier and gives a slightly better Strength boosts for her than Rinkah does.
Hinata:
The one pairing that comes to mind right away is Hinata and Hana. One of Hinata's main issues is his Speed stat, but when paired up with Swordmaster Hana, she fixes this issue perfectly. Hinata also gives Hana more bulk when it comes to Defense, an issue she normally suffers from. She also ensures Hisame's Speed and Strength stats stay well.
Hinoka also works pretty well. Once again, she gives Hinata a good speed boost, but this time, Falcon Knight Hinoka also gives him a good Resistance boost as well, another stat Hinata is not particularly in strong due to his physical nature. In return, Swordmaster Hinata makes Hinoka even faster than she already is, while Master of Arms Hinata gives Hinoka a solid Strength and Defense boost, two stats that Hinoka could use some improvement on. She also gives Hisame a boost in Strength and some solid bulk to both Defense and Resistance. Their support conversations are also pretty good.
Subaki:
One of Subaki's main issues is his Strength stat, so Rinkah makes a great pair-up bot to fix that issue (as well as making him more tanky). However, Rinkah isn't the best mom for Caeldori.
Hinoka tends to be the one that most people recommend marrying Subaki too. Subaki's speed can be a little lackluster, but when paired with Hinoka, she gives him a really nice boost with that. The two also gain boosted mobility, and the resulting Caeldori gets really good stat growths all around, not to mention that she gets some considerable mods in her Defense and Resistance stats to make her more durable. Their supports are also pretty nice, particularly giving some backstory to Hinoka in her earlier days as a Pegasus Knight.
Subaki can also function pretty well as a Magic attacker, particularly if he has the Bolt Naginata (the new name for the Shock Stick). Just pair him up with someone that can boost his Magic stat, use Rally Magic on him, and he can use that Bolt Naginata to his advantage. Sakura particularly comes to mind. As an Onmyoji, Sakura gives some very nice boosts in Magic and Speed to Subaki, while Priestess Sakura also boosts Magic nicely but gives a better boost in Resistance as well. The resulting Caeldori also becomes a great user of the Bolt Naginata just like her father, in addition to getting some neat Defense mods from her mother. I really didn't learn about how good of a Magic attacker Subaki and Caeldori are until I married Subaki with Nyx in my Revelation playthrough, but looking back, I don't regret marrying Subaki with Sakura. Their support conversations are also pretty cute.
Hayato
Hayato tends to work the best with magic-oriented units, so the three that come to mind are Orochi, Felicia, and Sakura. Orochi was who I married Hayato with in my Birthright playthrough, and the two worked pretty well together. Hayato patched up Orochi's speed issue, while Orochi turned Rhajat into a magic nuke. Felicia works well for similar reasons, except she gives a much bigger boost in Speed than Orochi does.
Most people would recommend marrying Hayato with Sakura though, mostly because the stat growths and mods tend to be the best for Rhajat when Sakura is her mother. Support conversation-wise, they are pretty cute together as well.
Silas
I married him with Hinoka in my Birthright playthrough, and they worked pretty well together. Hinoka fixed his Speed issue, while Silas gave her more bulk. Hinoka also gave Sophie some goods mods, particularly in Strength, Speed, Skill, and Resistance.
Hana works very well with Silas for similar reasons. Hana gives Silas the speed he needs, while Silas gives her better bulk. She also gives Sophie slightly better mods in Skill and Speed than Hinoka does.
Kaze
Mozu all the way for this one. Mozu gives Midori a pretty good Luck growth mod that allows for Miracle activations to happen quite frequently (and it is further boosted by Midori's personal skill). Mozu can also pass down Quick Draw if she is reclassed into an Archer-class early enough, though passing down Aptitude is also a very good option (the former skill is mainly useful for Midori if you want to keep her as a Merchant, which uses bows). Mozu also gives Midori great Speed mods as well.
In terms of a pair-up bot, Rinkah does a good job fixing Kaze's Strength issue, but when it comes to achieving an S-Support, you're better off pairing Kaze with Mozu for reasons previously stated.
Jakob
I didn't use Jakob until I played Revelation, but I married him with Kagero there. She makes his speed more manageable, while he gave her a bit more bulk and Strength thanks to his Great Knight class (his secondary class option, and the one I recommend switching him too when you have the chance). Kagero also gives Jakob's son, Dwyer, a really nice Strength boost, which is especially good since him and Jakob are meant to be physical units. This allowed Dwyer to make a pretty good Butler with the skills Lethality and Luna from his parents. I could've even turned him into a Master Ninja if I wanted to make him even better.
Azura also makes a good mother for Dwyer from what I've heard. She doesn't give as a high of a Strength mod that Kagero provides, but Azura does provide a really nice Speed mod as well. The result allows Dwyer to make a pretty rockin' Butler once again in order to highlight his physical prowess.
TL;DR
Male Corrin x Azura
Male Corrin x Scarlet
Takumi x Oboro
Ryoma x Kagero
Ryoma x Rinkah
Saizo x Orochi
Saizo x Sakura
Saizo x Kagero
Azama x Felicia
Azama x Setsuna
Azama x Kagero
Kaden x Rinkah
Kaden x Setsuna
Hinata x Hana
Hinata x Hinoka
Subaki x Hinoka
Subaki x Sakura
Hayato x Sakura
Hayato x Orochi
Hayato x Felicia
Silas x Hinoka
Silas x Hana
Kaze x Mozu
Jakob x Kagero
Jakob x Azura
These are all the options that I recommend.